Dawn: silence some warnings on win-clang.

Change-Id: Ifcab9738b5e1d17ed71e26fa30bb34951e421567
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249126
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>
1 file changed