net: ti: am65-cpsw-nuss: fix wrong devlink release order

The commit that introduced devlink support released devlink resources in
wrong order, that made an unwind flow to be asymmetrical. In addition,
the am65-cpsw-nuss used internal to devlink core field - registered.

In order to fix the unwind flow and remove such access to the
registered field, rewrite the code to call devlink_port_unregister only
on registered ports.

Fixes: 58356eb3 ("net: ti: am65-cpsw-nuss: Add devlink support")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>