net/mlx4_core: fix a memory leak bug.

In function mlx4_opreq_action(), pointer "mailbox" is not released,
when mlx4_cmd_box() return and error, causing a memory leak bug.
Fix this issue by going to "out" label, mlx4_free_cmd_mailbox() can
free this pointer.

Fixes: fe6f700d ("net/mlx4_core: Respond to operation request by firmware")
Signed-off-by: NQiushi Wu <wu000273@umn.edu>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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

@@ -2734,7 +2734,7 @@ void mlx4_opreq_action(struct work_struct *work)
 		if (err) {
 			mlx4_err(dev, "Failed to retrieve required operation: %d\n",
 				 err);
-			return;
+			goto out;
 		}
 		MLX4_GET(modifier, outbox, GET_OP_REQ_MODIFIER_OFFSET);
 		MLX4_GET(token, outbox, GET_OP_REQ_TOKEN_OFFSET);