Before calling init_hwif_default, ide_unregister gets lock ide_lock and
disables irq. init_hwif_default calls ide_default_io_base which calls
pci_get_device and later pci_get_subsys tries to apply for semaphore
pci_bus_sem and goes to sleep.
Mostly, pci_get_device should be called when irq is turned on.
ide_default_io_base just needs find if list pci_devices is empty.