pciehp: use get_service_data

Current pciehp driver saves its private data pointer into pci_dev
structure using pci_set_drvdata()/pci_get_drvdata(). But because
pciehp is not a pci device driver but a PCI Express service driver, it
should save its private data pointer into pcie_device structure using
set_service_data()/get_service_data().

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