Fix determining max combined uniform blocks The previous code was using a completely unrelated variable to compute max combined uniform blocks limit. BUG=angleproject:2099 Change-Id: I9e56b50a92790f525dda50adca52b6ac5edfc95a Reviewed-on: https://chromium-review.googlesource.com/562276 Commit-Queue: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Corentin Wallez <cwallez@chromium.org>