Migrate gamma grad from CUDA_tensor_apply3 to TensorIterator (#34020)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/34020
Test Plan: Imported from OSS
Differential Revision: D20196083
Pulled By: VitalyFedyunin
fbshipit-source-id: 8659bc004678a656071263c94e929f2e1a686812
