Cleanup nccl.cpp (#45899)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45899
Use function polymorphism to avoid repeated casts
I.e. instead of using `NCCL_CHECK(from_nccl_result(` add variant of the function that takes `ncclResult_t` as input argument
Add non-pointer variant of `to_nccl_comm` to avoid `*to_nccl_comm(&comm)` pattern
Test Plan: Imported from OSS
Reviewed By: walterddr
Differential Revision: D24138012
Pulled By: malfet
fbshipit-source-id: 7f62a03e108cbe455910e86e894afdd1c27e8ff1
