net/mlx4_core: Fix to clean devlink resources

This patch cleans devlink resources by calling devlink_port_unregister()
to avoid the following issues:

- Kernel panic when triggering reset flow.
- Memory leak due to unfreed resources in mlx4_init_port_info().

Fixes: 09d4d087

 ("mlx4: Implement devlink interface")
Signed-off-by: Kamal Heib <kamalh@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>