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: 381ceda8 ("powerpc/pseries/iommu: Make use of DDW for indirect mapping")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211020132315.2287178-3-aik@ozlabs.ru

arch/powerpc/platforms/pseries/iommu.c

@@ -1440,7 +1440,8 @@ static bool enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 		/* 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);