Correct VulkanBackendContext::fMaxAPIVersion passed to Skia

Unblocks http://review.skia.org/988938

Credit: Shahbaz Youssefi <syoussefi@google.com>

Bug: b/415173377
Flag: EXEMPT trivial fix for WIP code
Test: manually tested with blocked Skia CL patched on Pixel 9
Change-Id: I301f5efd922434d28e21f1cfb0b5e241caed6959