minigbm: fix size_t type not found

BUG=b:24674340
TEST=build pass on kevin

Change-Id: Idd780ee5e99e864ed0f97503e7b38673761201e8
Reviewed-on: https://chromium-review.googlesource.com/422808
Commit-Ready: Heng-ruey Hsu <henryhsu@chromium.org>
Tested-by: Heng-ruey Hsu <henryhsu@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
1 file changed