[MIPS] PCI: Make dev pointer argument of pcibios_map_irq const.

This is to break the code of people who think they are supposed to scribble
into the pci device structure - it's off limits.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/pci/pci-ip27.c b/arch/mips/pci/pci-ip27.c
index 405ce01..a322543 100644
--- a/arch/mips/pci/pci-ip27.c
+++ b/arch/mips/pci/pci-ip27.c
@@ -134,7 +134,7 @@
  * A given PCI device, in general, should be able to intr any of the cpus
  * on any one of the hubs connected to its xbow.
  */
-int __devinit pcibios_map_irq(struct pci_dev *dev, u8 slot, u8 pin)
+int __devinit pcibios_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
 {
 	struct bridge_controller *bc = BRIDGE_CONTROLLER(dev->bus);
 	int irq = bc->pci_int[slot];