serial: sunzilog: 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/20221019091151.6692-40-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sunzilog.c

@@ -508,8 +508,7 @@ static void sunzilog_transmit_chars(struct uart_sunzilog_port *up,
 	ZSDELAY();
 	ZS_WSYNC(channel);
 
-	xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-	up->port.icount.tx++;
+	uart_xmit_advance(&up->port, 1);
 
 	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
 		uart_write_wakeup(&up->port);
@@ -709,8 +708,7 @@ static void sunzilog_start_tx(struct uart_port *port)
 		ZSDELAY();
 		ZS_WSYNC(channel);
 
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		port->icount.tx++;
+		uart_xmit_advance(port, 1);
 
 		if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
 			uart_write_wakeup(&up->port);