Fixed a couple of Vulkan bugs

There was a bad test in GrVkImage, and the test in SkSLVariable was
allowing interface variables to be declared dead, which was probably
not a serious problem but was causing the debug layers to whine.

Bug: skia:8837
Change-Id: I233372ae45b575949b7c8f92b119b86e649f3142
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/199060
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
2 files changed