serial: stm32: 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/20221019091151.6692-35-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -596,8 +596,7 @@ static void stm32_usart_transmit_chars_pio(struct uart_port *port)
 		if (!(readl_relaxed(port->membase + ofs->isr) & USART_SR_TXE))
 			break;
 		writel_relaxed(xmit->buf[xmit->tail], port->membase + ofs->tdr);
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		port->icount.tx++;
+		uart_xmit_advance(port, 1);
 	}
 
 	/* rely on TXE irq (mask or unmask) for sending remaining data */
@@ -673,8 +672,8 @@ static void stm32_usart_transmit_chars_dma(struct uart_port *port)
 
 	stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAT);
 
-	xmit->tail = (xmit->tail + count) & (UART_XMIT_SIZE - 1);
-	port->icount.tx += count;
+	uart_xmit_advance(port, count);
+
 	return;
 
 fallback_err: