This corrects the naming style for this constant variable. Also updates
many usages in TextureD3D.cpp and TextureGL.cpp.

Bug: angleproject:2470
Change-Id: I029dd98e925cabf23a4bb26467a62afe6c5bb6e0
Reviewed-on: https://chromium-review.googlesource.com/1220726Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>