Fix bug in non_blocking copy (#20305)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20305
ghimport-source-id: eb3dacb10fd93bbb5a6bbe078ed1ec842163d0e6
Differential Revision: D15276094
Pulled By: li-roy
fbshipit-source-id: 4728f419aa050e6c94a4f62231fa1a86caa556a7
