serial: xuartps: 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/20221019091151.6692-44-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/xilinx_uartps.c

@@ -326,9 +326,7 @@ static void cdns_uart_handle_tx(void *dev_id)
 	       !(readl(port->membase + CDNS_UART_SR) & CDNS_UART_SR_TXFULL)) {
 
 		writel(xmit->buf[xmit->tail], port->membase + CDNS_UART_FIFO);
-
-		port->icount.tx++;
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+		uart_xmit_advance(port, 1);
 		numbytes--;
 	}