dm thin: use __blkdev_issue_discard for async discard support

With commit 38f2525533 ("block: add __blkdev_issue_discard") DM thinp
no longer needs to carry its own async discard method.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Mike Snitzer 2016-05-02 20:16:21 -04:00
commit 3dba53a958