[POWERPC] cell: Enable spider workarounds on all PCI buses

Don't limit spider I/O workarounds to the first two buses.
The IBM Cell blade has three of them (one PCI, two PCIe)
and we want to handle them all.

Signed-off-by: Jens Osterkamp <jens@de.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>