fix docs mistakes in lr_scheduler.MultiplicativeLR (#33805)
Summary:
This PR is referenced to an issue: [The docs of `MultiplicativeLR` use `LambdaLR` as example](https://github.com/pytorch/pytorch/issues/33752#issue-570374087)
https://github.com/pytorch/pytorch/issues/33752
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33805
Differential Revision: D20121314
Pulled By: mruberry
fbshipit-source-id: 5afa63bbe83d35ce4e55705b8cbd96326a907651
