watchdog: core: Make dt "timeout-sec" property work on drivers w/out min/max

It is valid for a watchdog driver to have 0 for a "min" and "max"
timeout if the driver doesn't need the core to enforce the concepts of
min and max.  The s3c2410_wdt driver is one such driver.  Specifically
it can be hard for that driver to come up with a static "max" on all
platforms without a lot more information since the input clock on
S3C2410 and S3C2440 can change with DVFS.

As written, watchdog_init_timeout() will not ever read "timeout-sec"
on these drivers since watchdog_timeout_invalid() will _never_ return
true.  Change to not consider a timeout_parm of 0 as valid even if
min/max aren't specified by the driver.  Also handle the case when
there is no min/max and no "timeout-sec" property.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/watchdog_core.c

@@ -78,7 +78,7 @@ int watchdog_init_timeout(struct watchdog_device *wdd,
 	watchdog_check_min_max_timeout(wdd);
 
 	/* try to get the timeout module parameter first */
-	if (!watchdog_timeout_invalid(wdd, timeout_parm)) {
+	if (!watchdog_timeout_invalid(wdd, timeout_parm) && timeout_parm) {
 		wdd->timeout = timeout_parm;
 		return ret;
 	}
@@ -89,7 +89,7 @@ int watchdog_init_timeout(struct watchdog_device *wdd,
 	if (dev == NULL || dev->of_node == NULL)
 		return ret;
 	of_property_read_u32(dev->of_node, "timeout-sec", &t);
-	if (!watchdog_timeout_invalid(wdd, t))
+	if (!watchdog_timeout_invalid(wdd, t) && t)
 		wdd->timeout = t;
 	else
 		ret = -EINVAL;