[fbsync] Make nvjpeg handle creation once_flag static (#5713)

Reviewed By: NicolasHug

Differential Revision: D35393163

fbshipit-source-id: 339bd0dd1ab3f61d32b154a937a9968bdbd54dbf

Author: datumbox

torchvision/csrc/io/image/cuda/decode_jpeg_cuda.cpp

@@ -71,7 +71,7 @@ torch::Tensor decode_jpeg_cuda(
   at::cuda::CUDAGuard device_guard(device);
 
   // Create global nvJPEG handle
-  std::once_flag nvjpeg_handle_creation_flag;
+  static std::once_flag nvjpeg_handle_creation_flag;
   std::call_once(nvjpeg_handle_creation_flag, []() {
     if (nvjpeg_handle == nullptr) {
       nvjpegStatus_t create_status = nvjpegCreateSimple(&nvjpeg_handle);