MIPS: avoid possible resource conflict in register_pci_controller

MIPS: avoid possible resource conflict in register_pci_controller

The IO and memory resources of a PCI controller
might already have a parent resource set when
they are passed to 'register_pci_controller'.

If the parent resource is set, the request_resource
call will fail due to resource conflict and the
current code will not be able to register the
PCI controller.

Use the parent resource if it is available in the
request_resource call to avoid the isssue.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/4910/
Signed-off-by: John Crispin <blogic@openwrt.org>