pci: remove pci_sub_bus() by open coding. Because pci_sub_bus() is used only once so eliminate it by open coding as suggested by "Michael S. Tsirkin" <mst@redhat.com>. Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>