Tests dEQP-EGL.functional.fence_sync.* can cause SyncHelper::clientWait
to be called with a null contextVk which we were trying to deference to
get to the renderer. We have a pointer to the renderer already so just
use that.

Bug: b/154030730
Change-Id: If64ec2c960f39b893d2e47a11638d16f830aecfd
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2493181
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>