PCI: Wrong register used to check pending traffic

The incorrect register offset is passed to pci_wait_for_pending(), which is
caused by commit 157e876f ("PCI: Add pci_wait_for_pending() (refactor
pci_wait_for_pending_transaction())").

Fixes: 157e876f

 ("PCI: Add pci_wait_for_pending() (refactor pci_wait_for_pending_transaction())
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Alex Williamson <alex.williamson@gmail.com>
CC: stable@vger.kernel.org	# v3.14+