loop: don't update discard limits from loop_set_status

loop_set_status doesn't change anything relevant to the discard and
write_zeroes setting, so don't bother calling loop_config_discard.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20231227082020.249427-1-hch@lst.de


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