ionic: cleanly release devlink instance

The failure to register devlink will leave the system with dangled
devlink resource, which is not cleaned if devlink_port_register() fails.

In order to remove access to ".registered" field of struct devlink_port,
require both devlink_register and devlink_port_register to success and
check it through device pointer.

Fixes: fbfb8031 ("ionic: Add hardware init and device commands")
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Acked-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>