Staging: ipack/devices/ipoctal: change exiting procedure

The ipoctal devices can be uninstalled from the ipack_driver_unregister()
call as the device model calles the bus's .remove() function for each device
registered by the driver and it will execute the .remove() function of the
ipoctal driver.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>