spapr_pci: use memory_region_add_subregion() with DMA windows

Passing a null priority to memory_region_add_subregion_overlap() is
strictly equivalent to calling memory_region_add_subregion().

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
index d84abf1..d258bc0 100644
--- a/hw/ppc/spapr_pci.c
+++ b/hw/ppc/spapr_pci.c
@@ -1752,8 +1752,8 @@
                        i, sphb->dtbusname);
             return;
         }
-        memory_region_add_subregion_overlap(&sphb->iommu_root, 0,
-                                            spapr_tce_get_iommu(tcet), 0);
+        memory_region_add_subregion(&sphb->iommu_root, 0,
+                                    spapr_tce_get_iommu(tcet));
     }
 
     sphb->msi = g_hash_table_new_full(g_int_hash, g_int_equal, g_free, g_free);