watchdog: mtk_wdt: signedness bug in mtk_wdt_start()

"ret" should be signed for the error handling to work correctly.  This
doesn't matter much in real life since mtk_wdt_set_timeout() always
succeeds.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-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

@@ -133,7 +133,7 @@ static int mtk_wdt_start(struct watchdog_device *wdt_dev)
 	u32 reg;
 	struct mtk_wdt_dev *mtk_wdt = watchdog_get_drvdata(wdt_dev);
 	void __iomem *wdt_base = mtk_wdt->wdt_base;
-	u32 ret;
+	int ret;
 
 	ret = mtk_wdt_set_timeout(wdt_dev, wdt_dev->timeout);
 	if (ret < 0)