Update cuda.get/set_rng_state doc (#14324)
Summary:
Now that `cuda.get/set_rng_state` accept `device` objects, the default value should be an device object, and doc should mention so.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/14324
Reviewed By: ezyang
Differential Revision: D13528707
Pulled By: soumith
fbshipit-source-id: 32fdac467dfea6d5b96b7e2a42dc8cfd42ba11ee
