Fix some unused variable warnings and make some stuff const in ReplicationPadding.cu (#70998)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/70998
Test Plan: Sandcastle
Reviewed By: malfet
Differential Revision: D33460035
fbshipit-source-id: bdf70fd04cce40a2a8d60c2c405f8d6cee9127e5
