serial: dz: 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/20221019091151.6692-2-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/dz.c

@@ -279,9 +279,8 @@ static inline void dz_transmit_chars(struct dz_mux *mux)
 	 * so we go one char at a time) :-<
 	 */
 	tmp = xmit->buf[xmit->tail];
-	xmit->tail = (xmit->tail + 1) & (DZ_XMIT_SIZE - 1);
 	dz_out(dport, DZ_TDR, tmp);
-	dport->port.icount.tx++;
+	uart_xmit_advance(&dport->port, 1);
 
 	if (uart_circ_chars_pending(xmit) < DZ_WAKEUP_CHARS)
 		uart_write_wakeup(&dport->port);