serial: sh-sci: Fix TX buffer mapping leak

The mapped transmit buffer is never unmapped. This leaks quite some
mappings, as the mapping is done in uart_ops.startup(), i.e. every time
the device is opened. Unmap the buffer on device close.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -1384,6 +1384,8 @@ static void sci_tx_dma_release(struct sci_port *s, bool enable_pio)
 
 	s->chan_tx = NULL;
 	s->cookie_tx = -EINVAL;
+	dma_unmap_single(chan->device->dev, s->tx_dma_addr, UART_XMIT_SIZE,
+			 DMA_TO_DEVICE);
 	dma_release_channel(chan);
 	if (enable_pio)
 		sci_start_tx(port);