[pytorch] Fix compiler warnings from conv.h (#56181)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56181
Need to change to size_t vs size_t:
Reviewed By: ezyang
Differential Revision: D27800849
fbshipit-source-id: 25f744128eb8750c382dc967a99af3c9f16247d9
