Fix signedness of format string.

Change-Id: I54fd8ba274b6b8f337e6b6461f594393259c779d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/855438
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Nicolette Prevost <nicolettep@google.com>
Commit-Queue: Nicolette Prevost <nicolettep@google.com>
1 file changed