test: fix cuda build

modules/cudaoptflow/test/test_optflow.cpp

@@ -46,6 +46,8 @@
 
 using namespace cvtest;
 
+namespace {
+
 //////////////////////////////////////////////////////
 // BroxOpticalFlow
 
@@ -401,4 +403,6 @@ INSTANTIATE_TEST_CASE_P(CUDA_OptFlow, OpticalFlowDual_TVL1, testing::Combine(
     ALL_DEVICES,
     testing::Values(Gamma(0.0), Gamma(1.0))));
 
-#endif // HAVE_CUDA
+} // namespace
+
+#endif // HAVE_CUDA