sc16is7xx: missing unregister/delete driver on error in sc16is7xx_init()

Add the missing uart_unregister_driver() and i2c_del_driver() before return
from sc16is7xx_init() in the error handling case.

Signed-off-by: Mao Wenan <maowenan@huawei.com>
Reviewed-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>