Fixed docs for forward_ad.make_dual (#71159)
Summary:
Minor docs change.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71159
Reviewed By: mruberry
Differential Revision: D33530031
Pulled By: albanD
fbshipit-source-id: e0bbe3a29a7de675fa4c9bf90976616f0e093f74
