[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-ddb5477.c b/arch/mips/pci/pci-ddb5477.c
index d071bc3..7363e18 100644
--- a/arch/mips/pci/pci-ddb5477.c
+++ b/arch/mips/pci/pci-ddb5477.c
@@ -131,7 +131,7 @@
 	/* SLOT: 20, AD:31 */ VRC5477_IRQ_IOPCI_INTA, /* vrc5477 usb host */
 };
 
-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)
 {
 	int slot_num;
 	unsigned char *slot_irq_map;