OF: PCI: const usage needed by MIPS

On MIPS we want to call of_irq_map_pci from inside

arch/mips/include/asm/pci.h:extern int pcibios_map_irq(
				const struct pci_dev *dev, u8 slot, u8 pin);
For this to work we need to change several functions to const usage.

Signed-off-by: John Crispin <blogic@openwrt.org>
Cc: linux-pci@vger.kernel.org
Cc: devicetree-discuss@lists.ozlabs.org
Cc: linux-mips@linux-mips.org
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Patchwork: https://patchwork.linux-mips.org/patch/3710/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>