Minor cleanup to change funciton signatures of vulkan specific methods in
MemoryObjectVk & SemaphoreVk.

Bug: angleproject:2475
Change-Id: I230664548004ebc48b559e0f25264ea948ce5a1f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2067500
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>