build: fix warnings

[tomoaki0705]

Pull Request Readiness Checklist

similar to #3417, but this one starts from 4.x

FilterMode, cudaTextureAddressMode, cudaTextureReadMode)’:
/opencv_contrib/modules/cudev/include/opencv2/cudev/ptr2d/texture.hpp:254:99: warning: declaration of ‘xoff’ shadows a member of ‘cv::cudev::TextureOff<T, R>’ [-Wshadow]
  254 |             const cudaTextureAddressMode addressMode = cudaAddressModeClamp, const cudaTextureReadMode readMode = cudaReadModeElementType) :
      |                                                                                                   ^
/opencv_contrib/modules/cudev/include/opencv2/cudev/ptr2d/texture.hpp:267:14: note: shadowed declaration is here
  267 |         int xoff = 0;
      |             ^~~~
/opencv_contrib/modules/cudev/include/opencv2/cudev/ptr2d/texture.hpp:254:99: warning: declaration of ‘yoff’ shadows a member of ‘cv::cudev::TextureOff<T, R>’ [-Wshadow]
  254 |             const cudaTextureAddressMode addressMode = cudaAddressModeClamp, const cudaTextureReadMode readMode = cudaReadModeElementType) :
      |                                                                                                   ^
/opencv_contrib/modules/cudev/include/opencv2/cudev/ptr2d/texture.hpp:268:5: note: shadowed declaration is here
  268 |         int yoff = 0;
      |             ^~~~

For the warning message below, I'm not that sure if it makes impact on performance

/opencv_contrib/modules/xfeatures2d/src/cuda/surf.cu(237): warning: dynamic initialization in unreachable code
          detected during:
            instantiation of "__nv_bool cv::cuda::device::surf::Mask<useMask>::check(int, int, int) [with useMask=false]" 
(302): here
            instantiation of "void cv::cuda::device::surf::icvFindMaximaInLayer(T, cv::cuda::PtrStepf, cv::cuda::PtrStepf, int4 *, unsigned int *) [with T=cv::cuda::device::surf::Mask<false>]" 
(376): here

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

force_builders=Custom
buildworker:Custom=linux-1
docker_image:Custom=ubuntu-cuda:16.04