Update embedding renorm comment to reference fixed issue (#29140)
Summary:
Address last comment in https://github.com/pytorch/pytorch/issues/28546
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29140
Differential Revision: D18915091
Pulled By: albanD
fbshipit-source-id: 756ff5bb6a92d47c80aa9f96ff6f0edea5fd24de
