Fix TypeScript readonly error location (#9887)

packages/babel-parser/src/plugins/typescript.js

@@ -743,7 +743,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
           return;
         default:
           this.raise(
-            node.operator,
+            node.start,
             "'readonly' type modifier is only permitted on array and tuple literal types.",
           );
       }