serial: sunsab: 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/20221019091151.6692-38-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sunsab.c

@@ -266,8 +266,7 @@ static void transmit_chars(struct uart_sunsab_port *up,
 	for (i = 0; i < up->port.fifosize; i++) {
 		writeb(xmit->buf[xmit->tail],
 		       &up->regs->w.xfifo[i]);
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		up->port.icount.tx++;
+		uart_xmit_advance(&up->port, 1);
 		if (uart_circ_empty(xmit))
 			break;
 	}
@@ -453,8 +452,7 @@ static void sunsab_start_tx(struct uart_port *port)
 	for (i = 0; i < up->port.fifosize; i++) {
 		writeb(xmit->buf[xmit->tail],
 		       &up->regs->w.xfifo[i]);
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		up->port.icount.tx++;
+		uart_xmit_advance(&up->port, 1);
 		if (uart_circ_empty(xmit))
 			break;
 	}