block: move {bdev,queue_limit}_discard_alignment out of line

No need to inline these fairly larger helpers.  Also fix the return value
to be unsigned, just like the field in struct queue_limits.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20220415045258.199825-22-hch@lst.de


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