hwmon: (w83793) Clean up a signedness issue

We cap the upper bound of "mtimeout" but since it's signed we should
check for negative values as well.  The mistake is harmless.  But I have
changed it to unsigned as a cleanup.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/w83793.c

@@ -1199,7 +1199,8 @@ static void w83793_init_client(struct i2c_client *client)
 
 static int watchdog_set_timeout(struct w83793_data *data, int timeout)
 {
-	int ret, mtimeout;
+	unsigned int mtimeout;
+	int ret;
 
 	mtimeout = DIV_ROUND_UP(timeout, 60);