block: return unsigned int from bdev_io_opt

block: return unsigned int from bdev_io_opt

The underlying limit is defined as an unsigned int, so return that from
bdev_io_opt as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20241119160932.1327864-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>