loop: fold loop_update_rotational into loop_reconfigure_limits

This prepares for moving the rotational flag into the queue_limits and
also fixes it for the case where the loop device is backed by a block
device.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20240617060532.127975-9-hch@lst.de


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