Fix texture errors on iOS Metal

Change-Id: I027b5e4a8ab737047e9fcd16be8b7597644c7dd6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/307569
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
3 files changed