Add missing return statements in testcase

Examples/test-suite/php_namewarn_rename.i

@@ -32,8 +32,8 @@
   };
 
   struct prev {
-    prev & operator++() { }
+    prev & operator++() { return *this; }
-    prev operator++(int) { }
+    prev operator++(int) { return *this; }
   };
 
 %}