[PyTorch] Use MaybeOwned and avoid resize in bmm_cuda (#56115)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56115
No reason to size it wrong and then resize it. Also, no reason to unconditionally go through the dispatcher.
ghstack-source-id: 128354110
Test Plan: Existing CI
Reviewed By: ngimel
Differential Revision: D27768757
fbshipit-source-id: 5dcb1fed5c5fa6707ee15359a26fde2a9a888b7f
