Staging: ipack/bridges/tpci200: Store the irq holder in slot_irq.

This way we do no longer need to keep a dangling pointer to struct
ipack_device in tpci200_slot after the device has been removed.

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