serial: MIPS: lantiq: use devm_iounmap instead of iounmap

port->membase was allocated using devm_ioremap_nocache, so ideally
we should unmap it using devm_iounmap. but it was using iounmap.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/lantiq.c

@@ -497,8 +497,10 @@ lqasc_type(struct uart_port *port)
 static void
 lqasc_release_port(struct uart_port *port)
 {
+	struct platform_device *pdev = to_platform_device(port->dev);
+
 	if (port->flags & UPF_IOREMAP) {
-		iounmap(port->membase);
+		devm_iounmap(&pdev->dev, port->membase);
 		port->membase = NULL;
 	}
 }