CONNECTOR: don't touch queue dev after decrement of ref count

cn_queue_free_callback() will touch 'dev'(i.e. cbq->pdev),
so it should be called before atomic_dec(&dev->refcnt).

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Adrian Bunk <bunk@kernel.org>