Rearrange Vulkan asserts for samplers

Change-Id: I6bbe834f0cf1ad725e1f3843b23fde958c749d8b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/277060
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed