net/mlx5_core: Avoid copying outbox in aysnc command completion

Avoid copying to the output buffer in cmd_exec since this is done after the
command is completed. Failure to do this may cause cases where the callback
handler is called before the copy done by cmd_exec which then overwrites it.
Reported-by: Tamer Hleihel <tamerh@mellanox.com>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx5/core/cmd.c

@@ -1236,6 +1236,7 @@ static int cmd_exec(struct mlx5_core_dev *dev, void *in, int in_size, void *out,
 		goto out_out;
 	}
 
+	if (!callback)
 		err = mlx5_copy_from_msg(out, outb, out_size);
 
 out_out: