serial: liteuart: Use uart_xmit_advance()

Take advantage of the new uart_xmit_advance() helper.
Acked-by: Gabriel Somlo <gsomlo@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-20-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/liteuart.c

@@ -136,8 +136,7 @@ static void liteuart_start_tx(struct uart_port *port)
 	} else if (!uart_circ_empty(xmit)) {
 		while (xmit->head != xmit->tail) {
 			ch = xmit->buf[xmit->tail];
-			xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-			port->icount.tx++;
+			uart_xmit_advance(port, 1);
 			liteuart_putchar(port, ch);
 		}
 	}