Avoid unnecessary tensor clone in Cloneable (#20995)
Summary:
As pointed out by SsnL in https://github.com/pytorch/pytorch/issues/20910, when clone destination is different from the module's device,
`Cloneable` currently calls `clone()` and then `to()` on every parameter and buffer, where the first clone is unnecessary.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20995
Differential Revision: D15517353
Pulled By: mrshenli
fbshipit-source-id: 6b6dc01560540a63845663f863dea0a948021fa5
