Change log message to debug VTS DTBO verify issue

Patch is intended to debug the DTBO verify  issue more conveniently,
it is better to replace __overlay__ node with fragment@x node,
like this :
ufdt_verify_fragment():failed to verify overlay node _overlay_ to target interrupt-controller@0xb220000
instead by:
ufdt_verify_fragment():failed to verify fragment node fragment@17 target_node interrupt-controller@0xb220000

Signed-off-by: gumingtao <gumingtao1225@gmail.com>
Signed-off-by: gumingtao <gumingtao@xiaomi.com>
Change-Id: I3a1616c2ab795f5c962043f44d7e3c6fe85ecb72
diff --git a/tests/libufdt_verify/ufdt_test_overlay.cpp b/tests/libufdt_verify/ufdt_test_overlay.cpp
index 2554d9d..71e888b 100644
--- a/tests/libufdt_verify/ufdt_test_overlay.cpp
+++ b/tests/libufdt_verify/ufdt_test_overlay.cpp
@@ -280,8 +280,8 @@
     bool result = ufdt_verify_overlay_node(target_node, overlay_node, tree, overlay_tree);
 
     if (!result) {
-        dto_error("failed to verify overlay node %s to target %s\n",
-                  ufdt_node_name(overlay_node), ufdt_node_name(target_node));
+        dto_error("failed to verify fragment node %s to target %s\n",
+                  ufdt_node_name(frag_node), ufdt_node_name(target_node));
         return OVERLAY_RESULT_VERIFY_FAIL;
     }