powerpc/iommu: Use coherent_dma_mask for alloc_coherent

The IOMMU code has been passing the dma-mask instead of the
coherent_dma_mask to the iommu allocator.  Coherent allocations should
be made using the coherent_dma_mask.

Also update the vio code to ensure the coherent_dma_mask is set. Without
this change drivers, such as ibmvscsi, fail to load with the corrected
dma_iommu_alloc_coherent().

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/dma-iommu.c b/arch/powerpc/kernel/dma-iommu.c
index 6e54a0f..e755415 100644
--- a/arch/powerpc/kernel/dma-iommu.c
+++ b/arch/powerpc/kernel/dma-iommu.c
@@ -19,7 +19,7 @@
 				      dma_addr_t *dma_handle, gfp_t flag)
 {
 	return iommu_alloc_coherent(dev, get_iommu_table_base(dev), size,
-				    dma_handle, device_to_mask(dev), flag,
+				    dma_handle, dev->coherent_dma_mask, flag,
 				    dev_to_node(dev));
 }