powerpc/PCI: convert to pci_create_root_bus()

Convert from pci_create_bus() to pci_create_root_bus().  This way the root
bus resources are correct immediately.  This patch doesn't fix a problem
because powerpc fixed the resources before scanning the bus, but it makes
powerpc more consistent with other architectures.

v2: fix build error with resource pointer passing

CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>