io_uring/rsrc: refactor io_rsrc_ref_quiesce

Refactor io_rsrc_ref_quiesce() by moving the first mutex_unlock(),
so we don't have to have a second mutex_unlock() further in the loop.
It prepares us to the next patch.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/65bc876271fb16bf550a53a4c76c91aacd94e52e.1681395792.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>