rt2x00: don't use to_pci_dev in rt2x00pci_uninitialize

Don't use to_pci_dev in rt2x00pci_uninitialize to get the allocated irq
as it won't work for platform devices (SoC). Instead, use the irq field
that's already used everywhere else.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>