Fix unused variable warning in lp_pool_op.cu (#71557)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/71557
Test Plan: Sandcastle
Reviewed By: malfet
Differential Revision: D33675165
fbshipit-source-id: d18f0833c8aeef7d2cc35919ebb328cac5a92db4
(cherry picked from commit bca6b8c8d164f0139ec7330d51e09bef7eba44ee)
