Fix stencil format mismatch in GrMtlPipelineState creation.

We can have a stencil attachment on the RenderTarget with stencil disabled.

Bug: skia:11392
Change-Id: Iefc661e9206eb859b02e91857f3682a525493df6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/380716
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
3 files changed