Vulkan: Fix last parameter of viewport driver uniform. This was introduced in a prior patch. Bug: angleproject:2717 Change-Id: I8f34377cbb9cbede4237efb1610400a8ed20ae2a Reviewed-on: https://chromium-review.googlesource.com/1131566 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>