pcmcia: allow for cb_irq to differ from pci_dev's irq in yenta_socket

cb_irq is presumed to be the same as the pci_dev's irq. This won't be
true any more as soon as we allow the ISA irq to be used for Cardbus
devices. Therefore, use the pci_dev's irq explicitely whenever we
care about it.

Part 2 of a series to allow the ISA irq to be used for Cardbus devices
if the socket's PCI irq is unusable.

[linux@dominikbrodowski.net: split up the original patch, commit message]

Signed-off-by: Jens Kuenzer <Jens.Kuenzer@fpga.homeip.net>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>