Fixed stub for AdamW (#34299)
Summary:
Fixes [https://github.com/pytorch/pytorch/issues/33757](https://github.com/pytorch/pytorch/issues/33757)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34299
Differential Revision: D20337844
Pulled By: ezyang
fbshipit-source-id: 54bf174a09b8db9bf6e0c3c717730dd7c795d76b
