nfp: do not handle nn->port defined case in nfp_net_get_phys_port_name()

If nn->port is defined it means that devlink_port has been registered
for this port as well. Devlink core is handling the port name
formatting.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>