serial: zs: Use uart_xmit_advance()

Take advantage of the new uart_xmit_advance() helper.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-45-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/zs.c

@@ -623,8 +623,7 @@ static void zs_raw_transmit_chars(struct zs_port *zport)
 
 	/* Send char.  */
 	write_zsdata(zport, xmit->buf[xmit->tail]);
-	xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-	zport->port.icount.tx++;
+	uart_xmit_advance(&zport->port, 1);
 
 	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
 		uart_write_wakeup(&zport->port);