fixed Metal release build

Bug: skia:
Change-Id: Iedb7a719f8993ed516bbad6ab3aaadcd4e14b207
Reviewed-on: https://skia-review.googlesource.com/c/162160
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
2 files changed