Fix a regression in 2.9.0 breaking validation while streaming

https://bugzilla.gnome.org/show_bug.cgi?id=684774
with help from Kjell Ahlstedt <kjell.ahlstedt@bredband.net>
diff --git a/SAX2.c b/SAX2.c
index a24abc8..3eea39a 100644
--- a/SAX2.c
+++ b/SAX2.c
@@ -2202,7 +2202,7 @@
 	  (ctxt->myDoc->intSubset->elements == NULL) &&
 	  (ctxt->myDoc->intSubset->attributes == NULL) &&
 	  (ctxt->myDoc->intSubset->entities == NULL)))) {
-	xmlErrValid(ctxt, XML_ERR_NO_DTD,
+	xmlErrValid(ctxt, XML_DTD_NO_DTD,
 	  "Validation failed: no DTD found !", NULL, NULL);
 	ctxt->validate = 0;
     }