Fix unused variable warning in EmbeddingBag.cu (#71589)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/71589
Test Plan: Sandcastle
Reviewed By: malfet
Differential Revision: D33692625
fbshipit-source-id: ad58e704de0202fb4f9e25c9c932f0cd5c832198
(cherry picked from commit ae77c2c8097f99f67fcec99c3c123b28139b3c3f)
