dbus: Remove unneeded typecast

This was triggering some gcc versions to warn about strict aliasing.
Since the typecast is not really needed here, the cleanest way to get
rid of the warnings is to just use the correct type for the local
variable.

wpa_supplicant/ctrl_iface_dbus_new_helpers.c

@@ -594,7 +594,7 @@ static DBusMessage * introspect(DBusMessage *message,
 	struct wpa_dbus_signal_desc *signal_dsc;
 	struct wpa_dbus_method_desc *method_dsc;
 	struct wpa_dbus_property_desc *property_dsc;
-	char *intro_str;
+	xmlChar *intro_str;
 	char **children;
 	int i, s;
 
@@ -798,7 +798,7 @@ static DBusMessage * introspect(DBusMessage *message,
 	dbus_free_string_array(children);
 
 
-	xmlDocDumpFormatMemory(doc, (xmlChar **) &intro_str, &s, 1);
+	xmlDocDumpFormatMemory(doc, &intro_str, &s, 1);
 
 	xmlFreeDoc(doc);