Direct3D: fix clang warning

Change-Id: Ifd909e237bc3ed1ee9bcafccb5ddcc849ba106e4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/405276
Auto-Submit: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed