[SPARC64]: Const'ify pci_iommu_ops.

Based upon a similar patch for x86_64 written by
Stephen Hemminger.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/asm-sparc64/pci.h b/include/asm-sparc64/pci.h
index b14a725b..47cea16 100644
--- a/include/asm-sparc64/pci.h
+++ b/include/asm-sparc64/pci.h
@@ -54,7 +54,7 @@
 	void (*dma_sync_sg_for_cpu)(struct pci_dev *, struct scatterlist *, int, int);
 };
 
-extern struct pci_iommu_ops *pci_iommu_ops;
+extern const struct pci_iommu_ops *pci_iommu_ops;
 
 /* Allocate and map kernel buffer using consistent mode DMA for a device.
  * hwdev should be valid struct pci_dev pointer for PCI devices.