null_blk: don't set the discard_alignment queue limit

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2083917



commit fb749a87
Author: Christoph Hellwig <hch@lst.de>
Date:   Mon Apr 18 06:53:06 2022 +0200

    null_blk: don't set the discard_alignment queue limit

    The discard_alignment queue limit is named a bit misleading means the
    offset into the block device at which the discard granularity starts.
    Setting it to the discard granularity as done by null_blk is mostly
    harmless but also useless.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
    Link: https://lore.kernel.org/r/20220418045314.360785-4-hch@lst.de


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

Signed-off-by: Ming Lei <ming.lei@redhat.com>