private void bt_Sua_Click(object sender, EventArgs e)
 {
     SP.update(txt_MaSP.Text, txt_TenSP.Text, cmb_LoaiSP.SelectedValue.ToString(), cmb_MaNCC.SelectedValue.ToString(), Rtxt_ThongTin.Text, txt_GiaBan.Text, txt_BaoHanh.Text);
     FSP.load();
     this.Close();
 }