Do not `std::move` returned value (#37891)
Summary:
This prevents compiler to use copy elision and triggers `redundant move in return statement` warning.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37891
Differential Revision: D21417998
Pulled By: malfet
fbshipit-source-id: 4008a6442cee3fe710c2da252b1bde7b4293b63f
