HifiGAN bug fixes
This pull request **introduces 1 alert** when merging 51b18761108fd3e3bb010ecdfc7de5dd9f58f1e7 into 646aff11aa788b7d874dae930ce6ffcd658c1f16 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-4f18e74fbecbcd7aa309fdb87b7e7f7dd90258ee)

**new alerts:**

* 1 for Unused import This pull request **introduces 1 alert** when merging 3f56fd44fed80502be09f8641d239930cb5add41 into 646aff11aa788b7d874dae930ce6ffcd658c1f16 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-d30e4dfd1c67b1be0980fa203da66149d80ad625)

**new alerts:**

* 1 for Unused import
Minor bug fixes for HifiGAN