Wextra fix for Tensorshape.cpp (#66320)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66320
Fixes
```
stderr: caffe2/aten/src/ATen/native/TensorShape.cpp:619:36: error: comparison of integers of different signs: 'size_t' (aka 'unsigned long') and 'long' [-Werror,-Wsign-compare]
for (size_t offset = 0; offset < numel; offset++) {
~~~~~~ ^ ~~~~~
stderr: caffe2/aten/src/ATen/native/TensorShape.cpp:619:36: error: comparison of integers of different signs: 'size_t' (aka 'unsigned long') and 'long' [-Werror,-Wsign-compare]
for (size_t offset = 0; offset < numel; offset++) {
~~~~~~ ^ ~~~~~
```
Test Plan: Sandcastle
Reviewed By: ngimel
Differential Revision: D31505374
fbshipit-source-id: 0fc393dacd72a8b29c0d82561f730cc047b38f0c
