powerpc/pseries/iommu: Use correct vfree for it_map

The it_map array is vzalloc'ed so use vfree() for it when creating
a huge DMA window failed for whatever reason.

While at this, write zero to it_map.

Fixes: 381ceda88c4c ("powerpc/pseries/iommu: Make use of DDW for indirect mapping")
Signed-off-by: Alexey Kardashevskiy <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/platforms/pseries/iommu.c

···
 		/* Keep default DMA window stuct if removed */
 		if (default_win_removed) {
 			tbl->it_size = 0;
-			kfree(tbl->it_map);
+			vfree(tbl->it_map);
+			tbl->it_map = NULL;
 		}
 
 		set_iommu_table_base(&dev->dev, newtbl);