MIPS: add dummy pci_load_of_ranges

The pci_load_of_ranges function is only available if
CONFIG_OF is selected. If the function is used without
CONFIG_OF being enabled it will cause a build error.

Add a dummy inline function to avoid this.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/4911/
Signed-off-by: John Crispin <blogic@openwrt.org>