Vulkan: Fix getting driver priority with async command queue Bug: angleproject:6245 Change-Id: Id6b6f83177dde85867685f814c5bdef4a5c97367 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3167212 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>