vulkan: switch (un)lock_queue to uint32_t

For consistency with both the Vulkan spec and the revised version of the lavu vulkan patchset. This was only chosen as int for compatibility with previous versions of that patchset.

This API has no users other than an experimental mpv branch, so it should be inconsequential to break. In either case, machine interpretation of non-negative int and uint32_t should be identical on all sane platforms.