serial: arc: Use uart_xmit_advance()

Take advantage of the new uart_xmit_advance() helper.

Signed-off-by: Ilpo Järvinen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/arc_uart.c

···
 		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);