[components][drivers][HUST CSE]修复serial_v2.c中可能产生的死循环 (#7394)

components/drivers/serial/serial_v2.c

@@ -691,11 +691,11 @@ static rt_err_t rt_serial_tx_enable(struct rt_device        *dev,
             serial->ops->control(serial,
                                 RT_DEVICE_CTRL_CONFIG,
                                 (void *)RT_SERIAL_TX_BLOCKING);
+            rt_memset(&tx_fifo->rb, RT_NULL, sizeof(tx_fifo->rb));
         }
 
         tx_fifo->activated = RT_FALSE;
         tx_fifo->put_size = 0;
-        rt_memset(&tx_fifo->rb, RT_NULL, sizeof(tx_fifo->rb));
         rt_completion_init(&(tx_fifo->tx_cpt));
         dev->open_flag |= RT_SERIAL_TX_BLOCKING;