Fix left shift ASAN problem

This should fix our new FSAA ASAN bot:
https://chromium-swarm.appspot.com/task?id=39446a25c7957710&refresh=10&show_raw=1&wide_logs=true
Bug: skia:7179
Change-Id: I1fcee6f7e3d8c8e3a646c67e41d4b6c19d372835
Reviewed-on: https://skia-review.googlesource.com/60702
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed