Suppress unsigned warning (#48272)
Summary:
Fixes a pointless comparison against zero warning that arises for some scalar types
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48272
Test Plan:
Arises with
```
xbuck test mode/dev-nosan //caffe2/torch/fb/sparsenn:gpu_test -- test_prior_correction_calibration_prediction_binary
```
Fixes issues raised by https://github.com/pytorch/pytorch/issues/47876 - `std::is_signed` was a poor choice `std::is_unsigned` is a better choice. Surprisingly, the two are non-reciprocal.
Reviewed By: zhangguanheng66
Differential Revision: D25256251
Pulled By: r-barnes
fbshipit-source-id: 31665f5b0bc7eebee7456b85c37c5bce3f738bea
