ia64/PCI: Clean up pci_scan_root_bus() usage

pci_scan_root_bus() already set bus->sysdata, so no need to explicitly
set it again in function sn_pci_controller_fixup().

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>