Use torch.ne instead of torch.nonzero in gradcheck (#37857)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/37857
Test Plan: Imported from OSS
Differential Revision: D21528484
Pulled By: anjali411
fbshipit-source-id: 2c43b4e4d484a943210dd9426c2e3ac1c30c8084
