driver: tty: add missing unregister in err case

when platform_driver_register broken, we should unregister ucc_uart_driver

Signed-off-by: Libo chen <libo.chen@huawei.com>
Acked-by: Timur Tabi <timur@tabi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>