[Serial] BUG Fix: data be send twice in mode that other than polling

components/drivers/serial/serial.c

@@ -431,14 +431,16 @@ static rt_size_t rt_serial_write(struct rt_device *dev,
 
     if (dev->open_flag & RT_DEVICE_FLAG_INT_TX)
     {
-		_serial_int_tx(serial, buffer, size);
+        return _serial_int_tx(serial, buffer, size);
     }
     else if (dev->open_flag & RT_DEVICE_FLAG_DMA_TX)
     {
-		_serial_dma_tx(serial, buffer, size);
+        return _serial_dma_tx(serial, buffer, size);
     }
-
+    else
+    {
         return _serial_poll_tx(serial, buffer, size);
+    }
 }
 
 static rt_err_t rt_serial_control(struct rt_device *dev,