[torchaudio] Fix torchaudio interface error (#2352)

[lsrami]

在torchaudio>2.0版本中移除了全局backend选项，采用在函数调用中backend参数指定后端，并将默认的backend设为ffmpeg

In 2.0, audio I/O backend dispatcher was introduced. Users can opt-in to using dispatcher by setting the environment variable TORCHAUDIO_USE_BACKEND_DISPATCHER=1.

In 2.1, the disptcher became the default mechanism for I/O.

In 2.2, the legacy global backend mechanism is removed. Utility functions get_audio_backend() and set_audio_backend() became no-op.

参考：TorchAudio Dispatcher Migration

[lsrami]

to fix #2352

[xingchensong]

great，thx

[Mddct]

great