PCI: pciehp: change name tag of "hpdriver_portdrv" variable

I think an appropriate name tag of "hpdriver_portdrv" variable
is "pciehp" rather than "hpdriver".

Signed-off-by: Taku Izumi <izumi.taku@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>