Fix compiler warning using mixed enum types

Started getting:

   error: bitwise operation between different enumeration types ('GrStencilSettings::(anonymous enum at ../../src/gpu/GrStencilSettings.h:134:5)' and 'GrStencilFlags') [-Werror,-Wanon-enum-enum-conversion]
       if ((kInvalid_PrivateFlag | kDisabled_StencilFlag) & (fFlags | that.fFlags)) {

after updating clang, which this CL fixes.

Change-Id: Ib2668e98298248ce5712d4ee9f125c78bf3445b2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/269140
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
2 files changed