Suppress /RTCc error about losing information during case to smaller type

Bug: skia:
Change-Id: I6c83504918fc1ff71f9153d3a2b02fa4c2d70871
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201646
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed