net/mlx4_core: Fix inaccurate return value of mlx4_flow_attach()

Adopt the "info: why not propagate 'ret' from parse_trans_rule()..."
suggestion made by the smatch semantic checker on:
drivers/net/ethernet/mellanox/mlx4/mcg.c:867 mlx4_flow_attach()
Signed-off-by: NEyal Perry <eyalpe@mellanox.com>
Signed-off-by: NAmir Vadai <amirv@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/mcg.c

@@ -897,7 +897,7 @@ int mlx4_flow_attach(struct mlx4_dev *dev,
 		ret = parse_trans_rule(dev, cur, mailbox->buf + size);
 		if (ret < 0) {
 			mlx4_free_cmd_mailbox(dev, mailbox);
-			return -EINVAL;
+			return ret;
 		}
 		size += ret;
 	}