vulkan: Fix 32-bit build for the new overlay layer

vulkan_core.h defines non-dispatchable handles as (struct object *) on 64-bit systems, but uint64_t on 32-bit systems. The former can be implicitly cast to void *, but the latter requires an explicit cast.

While here, %lu is the wrong format specifier for uint64_t on 32-bit systems, so use PRIu64, fixing a warning.

Reported-by: Mike Lothian mike@fireburn.co.uk