watchdog: mtk_wdt: Use MODE_KEY when stopping the watchdog

WDT_MODE value need to be or-ed with MODE_KEY when setting
watchdog mode. Add it to mtk_wdt_stop function, so that the
watchdog can be stopped (e.g. during suspend).
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Acked-by: Matthias Brugger <matthias.bgg@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/mtk_wdt.c

@@ -123,6 +123,7 @@ static int mtk_wdt_stop(struct watchdog_device *wdt_dev)
 
 	reg = readl(wdt_base + WDT_MODE);
 	reg &= ~WDT_MODE_EN;
+	reg |= WDT_MODE_KEY;
 	iowrite32(reg, wdt_base + WDT_MODE);
 
 	return 0;