Fix unused variable in validationES.cpp. Broken in 560a8d889b6866d7d29d. BUG=angle:571 Change-Id: Idb2414e11ad397cc45c2bdf5f357fd1b8e7fe6c2 Reviewed-on: https://chromium-review.googlesource.com/202602 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>