Fix hardsigmoid/hardswish for proper device dispatch. (#36704)
Summary:
https://github.com/pytorch/pytorch/pull/36351 make `hardsigmoid_backward` use tensoriterator but that can be done only after proper device dispatch.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36704
Differential Revision: D21068126
Pulled By: ailzhang
fbshipit-source-id: 6a6a74216f2b50fa7d15f692cd1583d3d233580a
