fix javadoc

Author: KeeProMise

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/protocolPB/AsyncRpcProtocolPBUtil.java

@@ -66,6 +66,8 @@ private AsyncRpcProtocolPBUtil() {}
    * @param call The IPC call encapsulating the RPC request.
    * @param response The function to apply to the response of the RPC call.
    * @param clazz The class object representing the type {@code R} of the response.
+   * @param <T> Type of the call's result.
+   * @param <R> Type of method return.
    * @return An object of type {@code R} that is the result of applying the response
    *         function to the RPC call result.
    * @throws IOException If an I/O error occurs during the asynchronous RPC call.