[SPARC64]: Fix 2 bugs in PCI Sabre bus scanning.

If we are on hummingbird, bus runs at 66MHZ.

pbm->pci_bus should be setup with the result of pci_scan_one_pbm()
or else we deref NULL pointers in the error interrupt handlers.

Signed-off-by: David S. Miller <davem@davemloft.net>