serial: digicolor: Use uart_xmit_advance()

Take advantage of the new uart_xmit_advance() helper.
Acked-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-15-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/digicolor-usart.c

@@ -202,8 +202,7 @@ static void digicolor_uart_tx(struct uart_port *port)
 
 	while (!uart_circ_empty(xmit)) {
 		writeb(xmit->buf[xmit->tail], port->membase + UA_EMI_REC);
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		port->icount.tx++;
+		uart_xmit_advance(port, 1);
 
 		if (digicolor_uart_tx_full(port))
 			break;