openvswitch: Fix ovs_vport_cmd_del return value on success

If the pointer does not represent an error then the PTR_ERR macro may still
return a nonzero value. The fix is the same as in ovs_vport_cmd_set.

Signed-off-by: Rich Lane <rlane@bigswitch.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index f996db3..5e275b9 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -1772,6 +1772,7 @@
 	if (IS_ERR(reply))
 		goto exit_unlock;
 
+	err = 0;
 	ovs_dp_detach_port(vport);
 
 	genl_notify(reply, genl_info_net(info), info->snd_portid,