loop: don't freeze the queue in loop_update_dio

All callers of loop_update_dio except for loop_configure already have the
queue frozen, and loop_configure works on an unbound device.  Remove the
superfluous recursive freezing in loop_update_dio and add asserts for the
locking and freezing state instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250110073750.1582447-8-hch@lst.de


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