serial: imx: Use uart_xmit_advance()

Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-18-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -563,8 +563,7 @@ static inline void imx_uart_transmit_buffer(struct imx_port *sport)
 		/* send xmit->buf[xmit->tail]
 		 * out the port here */
 		imx_uart_writel(sport, xmit->buf[xmit->tail], URTX0);
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		sport->port.icount.tx++;
+		uart_xmit_advance(&sport->port, 1);
 	}
 
 	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
@@ -590,9 +589,7 @@ static void imx_uart_dma_tx_callback(void *data)
 	ucr1 &= ~UCR1_TXDMAEN;
 	imx_uart_writel(sport, ucr1, UCR1);
 
-	/* update the stat */
-	xmit->tail = (xmit->tail + sport->tx_bytes) & (UART_XMIT_SIZE - 1);
-	sport->port.icount.tx += sport->tx_bytes;
+	uart_xmit_advance(&sport->port, sport->tx_bytes);
 
 	dev_dbg(sport->port.dev, "we finish the TX DMA.\n");