serial: arc: 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/20221019091151.6692-11-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/arc_uart.c

@@ -166,8 +166,7 @@ static void arc_serial_tx_chars(struct uart_port *port)
 		sent = 1;
 	} else if (!uart_circ_empty(xmit)) {
 		ch = xmit->buf[xmit->tail];
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		port->icount.tx++;
+		uart_xmit_advance(port, 1);
 		while (!(UART_GET_STATUS(port) & TXEMPTY))
 			cpu_relax();
 		UART_SET_DATA(port, ch);