Fix unused variable warning in LossCTC.cu (#71588)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/71588
Test Plan: Sandcastle
Reviewed By: malfet
Differential Revision: D33692622
fbshipit-source-id: b8ee83b775bc5b87f8ddc0936da2df24ab42420d
(cherry picked from commit b88934c5da4997fdef4f7f66b89fa8bee51c1525)
