Fix unused variable warning in Sorting.cu (#71555)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/71555
Test Plan: Sandcastle
Reviewed By: malfet, mruberry
Differential Revision: D33675174
fbshipit-source-id: c849b809d17d8c51b4ddba24ec5e2ae7bd1fa69a
(cherry picked from commit 440fca60be13135883f2cc3be98b078035906032)
