PCI: pciehp: fix irq initialization

Current pciehp driver gets irq number from pci_dev->irq. But because
pciehp driver is a pci express port service driver, it should get irq
number from pcie_device->irq.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>