dm snapshot: fix error return code in snapshot_ctr

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>
Cc: stable@vger.kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-snap.c

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index c0e0702..c434e5a 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1121,6 +1121,7 @@
 	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;
 	}