anv: Refactor anv_queue_finish()

anv: Refactor anv_queue_finish()

By moving vk_object_base_finish() to the end and putting the thread
clean-up in an if block we both better mimic anv_queue_init() and have a
more correct object destruction order.  It comes at the cost of a level
of indentation but that seems to actually make the function more clear.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8667>