devlink: Add missing genlmsg_cancel() in devlink_nl_sb_port_pool_fill()

If sb_occ_port_pool_get() failed in devlink_nl_sb_port_pool_fill(),
msg should be canceled by genlmsg_cancel().

Fixes: df38daf ("devlink: implement shared buffer occupancy monitoring interface")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Link: https://lore.kernel.org/r/20201113111622.11040-1-wanghai38@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/devlink.c

@@ -1448,7 +1448,7 @@ static int devlink_nl_sb_port_pool_fill(struct sk_buff *msg,
 		err = ops->sb_occ_port_pool_get(devlink_port, devlink_sb->index,
 						pool_index, &cur, &max);
 		if (err && err != -EOPNOTSUPP)
-			return err;
+			goto sb_occ_get_failure;
 		if (!err) {
 			if (nla_put_u32(msg, DEVLINK_ATTR_SB_OCC_CUR, cur))
 				goto nla_put_failure;
@@ -1461,8 +1461,10 @@ static int devlink_nl_sb_port_pool_fill(struct sk_buff *msg,
 	return 0;
 
 nla_put_failure:
+	err = -EMSGSIZE;
+sb_occ_get_failure:
 	genlmsg_cancel(msg, hdr);
-	return -EMSGSIZE;
+	return err;
 }
 
 static int devlink_nl_cmd_sb_port_pool_get_doit(struct sk_buff *skb,