pci: fix pci_find_bus(). When looking down child bus, it should look parent bridge's bus number, not child bus's. Optimized tail recursion and style fix. Cc: Blue Swirl <blauwirbel@gmail.com> Cc: "Michael S. Tsirkin" <mst@redhat.com> Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp> Signed-off-by: Blue Swirl <blauwirbel@gmail.com>