rename confusing lowp guard

Change-Id: I346429015e5f902b0a35663e140bb9a025c4220e
Reviewed-on: https://skia-review.googlesource.com/34680
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
2 files changed