message: tvl1 cuda optflow optimization
diff: @@ -162,7 +162,9 @@ namespace
  GpuMat p32_buf;
  GpuMat diff_buf;
  - GpuMat norm_buf;
  +
  + GpuMat diff_sum_dev;
  + Mat diff_sum_host;
  };
  void OpticalFlowDual_TVL1_Impl::calc(InputArray _frame0, InputArray _frame1, InputOutputArray _flow, Stream& stream)
  @@ -361,8 +363,11 @@ namespace
  estimateU(I1wx, I1wy, grad, rho_c, p11, p12, p21, p22, p31, p32, u1, u2, u3, diff, l_t, static_cast<float>(theta_), gamma_, calcError, stream);
  if (calcError)
  {
  + cuda::calcSum(diff, diff_sum_dev, cv::noArray(), _stream);
  + diff_sum_dev.download(diff_sum_host, _stream);
  _stream.waitForCompletion();
  - error = cuda::sum(diff, norm_buf)[0];
  +
  + error = diff_sum_host.at<double>(0,0);
  prevError = error;
  }
  else
  