openvswitch: Fix return value check in ovs_meter_cmd_features()

In case of error, the function ovs_meter_cmd_reply_start() returns
ERR_PTR() not NULL. The NULL test in the return value check should
be replaced with IS_ERR().

Fixes: 96fbc13d7e77 ("openvswitch: Add meter infrastructure")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/openvswitch/meter.c

@@ -166,7 +166,7 @@ static int ovs_meter_cmd_features(struct sk_buff *skb, struct genl_info *info)
 
 	reply = ovs_meter_cmd_reply_start(info, OVS_METER_CMD_FEATURES,
 					  &ovs_reply_header);
-	if (!reply)
+	if (IS_ERR(reply))
 		return PTR_ERR(reply);
 
 	if (nla_put_u32(reply, OVS_METER_ATTR_MAX_METERS, U32_MAX) ||