loop: allow loop_set_status to re-enable direct I/O

Unlike all other calls of (__)loop_update_dio, loop_set_status never
looks at the O_DIRECT flag of the backing file, and thus doesn't
re-enable direct I/O on an O_DIRECT backing file if e.g. the new block
size would allow it.  Fix that and remove the need for the separate
__loop_update_dio flag.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250110073750.1582447-7-hch@lst.de


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