[graphite] Fix unintentional switch fallthrough causing Debian build failures

Inadvertently introduced in https://skia-review.googlesource.com/c/skia/+/599345

Change-Id: Ie3e8c95466ac704a8743b588d0c272073d9d474a
Bug: b/253450161
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/605287
Commit-Queue: Nicolette Prevost <nicolettep@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
1 file changed