block: remove queue_discard_alignment

Just use bdev_alignment_offset in disk_discard_alignment_show instead.
That helpers is the same except for an always false branch that doesn't
matter in this slow path.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20220415045258.199825-20-hch@lst.de


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