serial: 8250_dma: terminate correct DMA in tx_dma_flush()

When flushing transmit side DMA, it is the transmit channel that should
be terminated, not the receive channel.

Fixes: 9e512ea ("serial: 8250: Fix fifo underflow on flush")
Cc: stable <[email protected]>
Reported-by: Wentao Guan <[email protected]>
Signed-off-by: John Keeping <[email protected]>
Reviewed-by: Ilpo Järvinen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: johnkeeping

drivers/tty/serial/8250/8250_dma.c

@@ -162,7 +162,7 @@ void serial8250_tx_dma_flush(struct uart_8250_port *p)
 	 */
 	dma->tx_size = 0;
 
-	dmaengine_terminate_async(dma->rxchan);
+	dmaengine_terminate_async(dma->txchan);
 }
 
 int serial8250_rx_dma(struct uart_8250_port *p)