Fix docstring for nn.MultiHeadAttention (#71100)
Summary:
Fixes nn.MultiHeadAttention's docstring problem reported at https://github.com/pytorch/pytorch/issues/70498.
cc albanD mruberry jbschlosser walterddr kshitij12345
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71100
Reviewed By: mruberry
Differential Revision: D33531726
Pulled By: albanD
fbshipit-source-id: d2aa8fa44d0f6b166a809b7e5ceee26efcbccf36
