Fix unused variable warning in DistanceKernel.cu (#71586)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/71586
Test Plan: Sandcastle
Reviewed By: malfet
Differential Revision: D33692618
fbshipit-source-id: 6265efc9b7106737ac8e70e36e611c8997572d5c
(cherry picked from commit 5b2699a0c72723314897d8ed04a63016b48daa90)
