Slight speed improvement in the Vulkan vertex array state change test.

Bug: angleproject:3014
Change-Id: I4a5cd26849cd247b7e67cd6bda083aabeb4e34c0
Reviewed-on: https://chromium-review.googlesource.com/c/1406890
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>