loop: fix queue freeze vs limits lock order

Match the locking order used by the core block code by only freezing
the queue after taking the limits lock using the
queue_limits_commit_update_frozen helper and document the callers that
do not freeze the queue at all.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20250110054726.1499538-12-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>