serial: altera_uart: call iounmap() at driver remove

The driver calls ioremap() in the probe function but doesn't call
iounmap() in the remove function correspondingly. Do so now.

Follow commit 5c9d6abed9e0 ("serial: altera_jtaguart: adding iounmap()")

Cc: Alexey Khoroshilov <[e-mail]>
Signed-off-by: Tobias Klauser <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/altera_uart.c

···
 	if (port) {
 		uart_remove_one_port(&altera_uart_driver, port);
 		port->mapbase = 0;
+		iounmap(port->membase);
 	}
 
 	return 0;