__blkdev_issue_discard_async() doesn't need to worry about further
splitting because the upper layer blkdev_issue_discard() will have
already handled splitting bios such that the bi_size isn't
overflowed.
Signed-off-by: NMike Snitzer <snitzer@redhat.com>
Acked-by: NJoe Thornber <ejt@redhat.com>