fixed unused function in case of unavailable CUDA

modules/core/src/cuda_host_mem.cpp

@@ -46,6 +46,7 @@
 using namespace cv;
 using namespace cv::cuda;
 
+#ifdef HAVE_CUDA
 namespace
 {
     size_t alignUpStep(size_t what, size_t alignment)
@@ -56,6 +57,7 @@ namespace
         return res;
     }
 }
+#endif
 
 void cv::cuda::CudaMem::create(int rows_, int cols_, int type_)
 {