serial: pch_uart: Use uart_xmit_advance()

Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-5-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/pch_uart.c

@@ -738,15 +738,12 @@ static void pch_dma_tx_complete(void *arg)
 {
 	struct eg20t_port *priv = arg;
 	struct uart_port *port = &priv->port;
-	struct circ_buf *xmit = &port->state->xmit;
 	struct scatterlist *sg = priv->sg_tx_p;
 	int i;
 
-	for (i = 0; i < priv->nent; i++, sg++) {
-		xmit->tail += sg_dma_len(sg);
-		port->icount.tx += sg_dma_len(sg);
-	}
-	xmit->tail &= UART_XMIT_SIZE - 1;
+	for (i = 0; i < priv->nent; i++, sg++)
+		uart_xmit_advance(port, sg_dma_len(sg));
+
 	async_tx_ack(priv->desc_tx);
 	dma_unmap_sg(port->dev, sg, priv->orig_nent, DMA_TO_DEVICE);
 	priv->tx_dma_use = 0;
@@ -843,8 +840,7 @@ static unsigned int handle_tx(struct eg20t_port *priv)
 
 	while (!uart_tx_stopped(port) && !uart_circ_empty(xmit) && fifo_size) {
 		iowrite8(xmit->buf[xmit->tail], priv->membase + PCH_UART_THR);
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		port->icount.tx++;
+		uart_xmit_advance(port, 1);
 		fifo_size--;
 		tx_empty = 0;
 	}