[fuzz] Make mock gpu fuzzer compatible with Vulkan

Change-Id: I857da21674db669d7f2766132e9909ccbcdc1c55
Bug: oss-fuzz:44132
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/502536
Reviewed-by: Robert Phillips <robertphillips@google.com>
2 files changed