microblaze/PCI: fix pci_bus_for_each_resource() usage

The pci_bus_for_each_resource() iterator sets "res" itself, so there's
no need to look it up in the bus->resource[] table.

Logically part of 89a74ecc and 8a66da71.

CC: Michal Simek <monstr@monstr.eu>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>