[PyTorch] Use .sizes() isntead of .size() in cat_serial_kernel_impl (#49371)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49371
As with previous diff, .sizes() is strictly more efficient.
ghstack-source-id: 118627223
Test Plan: internal benchmark
Differential Revision: D25546409
fbshipit-source-id: 196034716b6e11efda1ec8cb1e0fce7732d73eb4
