[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>

arch/mips/pci/fixup-atlas.c

@@ -58,7 +58,7 @@ static char irq_tab[][5] __initdata = {
 	{0,	0,	0,	0,	0 }	/* 21: Unused */
 };
 
-int __init pcibios_map_irq(struct pci_dev *dev, u8 slot, u8 pin)
+int __init pcibios_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
 {
 	return irq_tab[slot][pin];
 }