This should be %u not %d.

BUG=angleproject:1309

Change-Id: I1fe1b8df9ea4f9123fc05e9ff58afa1f7723692c
Reviewed-on: https://chromium-review.googlesource.com/636521Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>