parse.y: fix a wrong sizeof argument for ruby_sized_xfree

parse.y

@@ -5854,7 +5854,7 @@ vtable_free_gen(struct parser_params *p, int line, const char *name,
 	if (tbl->tbl) {
 	    ruby_sized_xfree(tbl->tbl, tbl->capa * sizeof(ID));
 	}
-	ruby_sized_xfree(tbl, sizeof(tbl));
+	ruby_sized_xfree(tbl, sizeof(*tbl));
     }
 }
 #define vtable_free(tbl) vtable_free_gen(p, __LINE__, #tbl, tbl)