Vulkan: Fix up varying component limits. We weren't subtracting reserved varying vectors from component limits. We also were using an incorrect value for fragment input components. Bug: angleproject:5496 Change-Id: I44fc3b2f15687f4dee7a1498d50378e69d74afe3 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2606536 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>