PCI: pciehp: fix possible endless loop in pcie_isr

PCI: pciehp: fix possible endless loop in pcie_isr

Fix possible endless loop in pcie_isr.

Currently, pcie_isr() (interrupt service routine of pciehp) can end up in an
endless loop if the Slot Status register is set again immediately after being
cleared. According to the past discussion (see below URL) this case can happen
if the power fault detected bit is set during handling.

http://sourceforge.net/mailarchive/message.php?msg_id=20051130135409.A14918%40unix-os.sc.intel.com

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