Fix performance regresion on Mali, while preserving sk_FragCoord.w

Bug: skia:
Change-Id: I9269288bbb861cd02efa7b5dfe2c9434ec39064e
Reviewed-on: https://skia-review.googlesource.com/c/174309
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
2 files changed