dm snapshot: fix error return code in snapshot_ctr

commit 09e8b813 upstream.

Return -ENOMEM instead of success if unable to allocate pending
exception mempool in snapshot_ctr.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/md/dm-snap.c

@@ -1117,6 +1117,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	s->pending_pool = mempool_create_slab_pool(MIN_IOS, pending_cache);
 	if (!s->pending_pool) {
 		ti->error = "Could not allocate mempool for pending exceptions";
+		r = -ENOMEM;
 		goto bad_pending_pool;
 	}