powerpc/iommu: Fix initialisation of DART iommu table

Commit d0847757 switched the generic
powerpc iommu backend code to use the it_page_shift field to determine
page size. Commit 3a553170 should have
initiliased this field for all platforms, however the DART iommu table
code was not updated.

This commit initialises the it_page_shift field to 4K for the DART
iommu.
Signed-off-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/sysdev/dart_iommu.c

@@ -292,6 +292,7 @@ static void iommu_table_dart_setup(void)
 	iommu_table_dart.it_offset = 0;
 	/* it_size is in number of entries */
 	iommu_table_dart.it_size = dart_tablesize / sizeof(u32);
+	iommu_table_dart.it_page_shift = IOMMU_PAGE_SHIFT_4K;
 
 	/* Initialize the common IOMMU code */
 	iommu_table_dart.it_base = (unsigned long)dart_vbase;