serial: cpm_uart: Use uart_xmit_advance()

Take advantage of the new uart_xmit_advance() helper.

Signed-off-by: Ilpo Järvinen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/cpm_uart/cpm_uart_core.c

···
 		p = cpm2cpu_addr(in_be32(&bdp->cbd_bufaddr), pinfo);
 		while (count < pinfo->tx_fifosize) {
 			*p++ = xmit->buf[xmit->tail];
-			xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-			port->icount.tx++;
+			uart_xmit_advance(port, 1);
 			count++;
 			if (xmit->head == xmit->tail)
 				break;