watchdog: wdt285: Fix variable type

Variable "new_margin" is checked in the function watchdog_ioctl()
to be non-negative, so change its type to "int".
Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/wdt285.c

@@ -139,9 +139,8 @@ static const struct watchdog_info ident = {
 static long watchdog_ioctl(struct file *file, unsigned int cmd,
 			   unsigned long arg)
 {
-	unsigned int new_margin;
 	int __user *int_arg = (int __user *)arg;
-	int ret = -ENOTTY;
+	int new_margin, ret = -ENOTTY;
 
 	switch (cmd) {
 	case WDIOC_GETSUPPORT: