Small adjustment after merging fix for bug#23651 "Server crashes when

trigger which uses stored function invoked from different connections"
into 5.1.

sql/item_func.cc

@@ -4852,7 +4852,7 @@ Item_func_sp::cleanup()
     result_field= NULL;
   }
   m_sp= NULL;
-  dummy_table->s= NULL;
+  dummy_table->alias= NULL;
   Item_func::cleanup();
 }