Return version from cuda version check (#2919)

Summary:
Return version from cuda version check so that we can display it in the test details

Pull Request resolved: https://github.com/pytorch/audio/pull/2919

Reviewed By: mthrok

Differential Revision: D42001252

Pulled By: atalman

fbshipit-source-id: 0d8fc3812a13fe098cdf8e0f3df7b66161ba3f95

torchaudio/_extension.py

@@ -130,6 +130,7 @@ def _check_cuda_version():
                 f"PyTorch has CUDA version {t_version} whereas TorchAudio has CUDA version {ta_version}. "
                 "Please install the TorchAudio version that matches your PyTorch version."
             )
+    return version
 
 
 _init_extension()