powerpc: kmalloc failure ignored in vio_build_iommu_table()

Prevent NULL dereference if kmalloc() fails.

Signed-off-by: Roel Kluin <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/kernel/vio.c

···
 		return NULL;
 
 	tbl = kmalloc(sizeof(*tbl), GFP_KERNEL);
+	if (tbl == NULL)
+		return NULL;
 
 	of_parse_dma_window(dev->dev.archdata.of_node, dma_window,
 			    &tbl->it_index, &offset, &size);