Fix signed/unsigned compiler warning.

Change-Id: Id82e8dba0d934f5c4bb2eefe1647839f25917898
Reviewed-on: https://swiftshader-review.googlesource.com/5150
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
2 files changed