remove a var for INT_TX.

components/drivers/serial/serial.c

@@ -146,9 +146,12 @@ static rt_err_t rt_serial_init(struct rt_device *dev)
 
         if (dev->flag & RT_DEVICE_FLAG_INT_TX)
         {
+			/* not supported yet */
+			/*
             serial->ops->control(serial, RT_DEVICE_CTRL_SET_INT, (void *)RT_NULL);
             serial_ringbuffer_init(serial->int_tx);
             serial->int_sending_flag = RT_FALSE;
+			*/
         }
 
         if (dev->flag & RT_DEVICE_FLAG_DMA_TX)