Upload gambar dengan ajax codeigniter

malam gan... saya upload gambar dengan ajax di codeigniter namun tersimpan didatabase keterangan nya You did not select a file to upload

sementara file gambar tersimpan ke folder...

mohon petunjuknya gan. terimakasih

SCRIPT MODEL UNTUK SIMPAN DATA
public function save($msg){

    $data = array(
      "no_lhp" => $this->input->post('no_lhp1'),
      "idskpd" => $this->input->post('idskpd'),
      "idpemeriksa" => $this->input->post('idpemeriksa'),
      "tgl_tlhp" => $this->input->post('tgl_tlhp'),
      "ket" => $this->input->post('ket'),
      "nominal" => format_num($this->input->post('nominal')),
      "status" => $this->input->post('status'),
      "idrekomendasi" => $this->input->post('idrekomendasi'),
      "filename"=>$msg
    );
//var_dump($data);
//die;
    $this->db->insert('tlhp',$data); // Untuk mengeksekusi perintah insert data

}
SCRIPT CONTROLLER UPLOAD GAMBAR
public function simpan(){
    $config['upload_path'] = './assets/document';
    $config['allowed_types'] = 'gif|jpg|png';
    $config['max_size']  = '1000';
    $config['max_width']  = '1024';
    $config['max_height']  = '768';

    $this->load->library('upload', $config);

    if ( ! $this->upload->do_upload('file')){
        //$status = "error";
        $msg = $this->upload->display_errors();
    }
    else{
        $dataupload = $this->upload->data();
       // $status = "success";
        $msg = $dataupload['file_name'];
        $this->Lhp_model->save($msg);
    }
    if($this->Lhp_model->validation("save")){ // Jika validasi sukses atau hasil validasi adalah true

      //die;
        $this->Lhp_model->save($msg); // Panggil fungsi save() yang ada di Lhp_model.php
        //$this->Lhp_model->save();

      $html = $this->load->view('admin/viewlhp', array('model'=>$this->Lhp_model->view()), true);
      $callback = array(
        'status'=>'sukses',
        'pesan'=>'Data berhasil disimpan',
        'html'=>$html
      );
    }else{
      $callback = array(
        'status'=>'gagal',
        'pesan'=>validation_errors()
      );
  }
    echo json_encode($callback);
    }
SCRIPT LINK SIMPAN DENGAN FILE AJAX YANG DIPANGGIL
$('#btn-simpan').click(function(){ // Ketika tombol simpan di klik
    $('#loading-simpan').show() // Munculkan loading simpan

            var file_data = $('#gambar').prop('files')[0];
            var form_data = new FormData();

            form_data.append('file', file_data);
            $.ajax({
                url: '<?php echo site_url("lhp/simpan") ?>', // point to server-side PHP script
                dataType: 'json',  // what to expect back from the PHP script, if anything
                cache: false,
                contentType: false,
                processData: false,
                data: form_data,
                type: 'post',
      beforeSend: function(e) {
        if(e && e.overrideMimeType) {
          e.overrideMimeType('application/jsoncharset=UTF-8')
        }
      },
      success: function(response){ // Ketika proses pengiriman berhasil
        $('#loading-simpan').hide() // Sembunyikan loading simpan

        if(response.status == 'sukses'){ // Jika Statusnya = sukses
          // Ganti isi dari div view dengan view yang diambil dari proses simpan.php
          $('#view').html(response.html)

          /*
          * Ambil pesan suksesnya dan set ke div pesan-sukses
          * Lalu munculkan div pesan-sukes nya
          * Setelah 10 detik, sembunyikan kembali pesan suksesnya
          */
          $('#pesan-sukses').html(response.pesan).fadeIn().delay(10000).fadeOut()

          $('#form-modal').modal('hide') // Close / Tutup Modal Dialog

          // Bersihkan teks saat modal di close
          document.getElementById("idrekomendasi").value = "";
          document.getElementById("no_lhp").value = "";
          document.getElementById("no_lhp1").value = "";
          document.getElementById("tgl_lhp").value = "";
          document.getElementById("idskpd").value = "";
          document.getElementById("idpemeriksa").value = "";
          document.getElementById("thn_periksa").value = "";
          document.getElementById("obyek_periksa").value = "";
          document.getElementById("uraian").value = "";
          document.getElementById("skpd").value = "";
          document.getElementById("pemeriksa").value = "";
        }else{ // Jika statusnya = gagal
          /*
          * Ambil pesan errornya dan set ke div pesan-error
          * Lalu munculkan div pesan-error nya
          */
          $('#pesan-error').html(response.pesan).show()
        }
      },
      error: function (xhr, ajaxOptions, thrownError) { // Ketika terjadi error
        alert(xhr.responseText) // munculkan alert
      }
    })
  })
SCRIPT AJAX DI FORM
 <script>
        $(document).on('click','#btn-simpan',function(e){
            e.preventDefault();
            var file_data = $('#gambar').prop('files')[0];
            var form_data = new FormData();

            form_data.append('file', file_data);
            $.ajax({
                url: '<?php echo site_url("lhp/simpan") ?>', // point to server-side PHP script
                dataType: 'json',  // what to expect back from the PHP script, if anything
                cache: false,
                contentType: false,
                processData: false,
                data: form_data,
                type: 'post',
                success: function(data,status){
                    //alert(php_script_response); // display response from the PHP script, if any
                    if (data.status!='error') {
                        $('#gambar').val('');
                        alert(data.msg);
                    }else{
                        alert(data.msg);
                    }
                }
            });
        })
    </script>