powerpc/PCI: Use list_for_each_entry() for bus traversal

Replace list_for_each() + pci_bus_b() with list_for_each_entry().

Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --cc arch/powerpc/kernel/pci_64.c
Simple merge

diff --cc arch/powerpc/platforms/pseries/pci_dlpar.c
Simple merge