Fix issue re: DDP and create_graph=True (#63831)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63831
Closes https://github.com/pytorch/pytorch/issues/63812
`at::mul_out` is not supported when `grad` itself requires grad, which is useful for computing higher order derivatives.
In this case, fall back to a mul + copy instead of mul_out.
ghstack-source-id: 136614644
Test Plan: UT
Reviewed By: SciPioneer
Differential Revision: D30505573
fbshipit-source-id: 83532b6207b3d80116fcc4dff0e5520d73b3454f
