IB/multicast: Check ib_find_pkey() return value

commit d3a2418e upstream.

This patch avoids that Coverity complains about not checking the
ib_find_pkey() return value.

Fixes: commit 547af765 ("IB/multicast: Report errors on multicast groups if P_key changes")
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/infiniband/core/multicast.c

@@ -516,8 +516,11 @@ static void join_handler(int status, struct ib_sa_mcmember_rec *rec,
 	if (status)
 		process_join_error(group, status);
 	else {
-		ib_find_pkey(group->port->dev->device, group->port->port_num,
-			     be16_to_cpu(rec->pkey), &pkey_index);
+
+		if (ib_find_pkey(group->port->dev->device,
+				 group->port->port_num, be16_to_cpu(rec->pkey),
+				 &pkey_index))
+			pkey_index = MCAST_INVALID_PKEY_INDEX;
 
 		spin_lock_irq(&group->port->lock);
 		group->rec = *rec;