Switch createAlphaClipMask to use kTopLeft

This makes createAlphaClipMask match createSoftwareClipMask

Bug: 854875
Change-Id: I92a81f5025a19548c6225f39c84b2b2f87c53550
Reviewed-on: https://skia-review.googlesource.com/137888
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Chris Dalton <csmartdalton@google.com>
1 file changed