net/mlx5e: Fix devlink port netdev unregistration sequence

In cited commit netdevice is registered after devlink port.

Unregistration flow should be mirror sequence of registration flow.
Hence, unregister netdevice before devlink port.

Fixes: 31e87b39

 ("net/mlx5e: Fix devlink port register sequence")
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>