watchdog: Always return time left until watchdog times out

watchdog: Always return time left until watchdog times out

The watchdog core knows when the most recent keepalive was sent. It also
knows the configured timeout. With that, it can always calculate and
return the time left until a watchdog times out, even if its driver does
not support it.

Convert watchdog_get_timeleft() into a void function. It never returns an
error after this patch is applied, so the error checks in the calling code
are now pointless and can be removed.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>