watchdog: wdat_wdt: Avoid unimplemented get_timeleft

As per the specification the action QUERY_COUNTDOWN_PERIOD is optional.
If the action is not implemented by the physical device the driver would
always report "0" from get_timeleft().
Avoid confusing userspace by only providing get_timeleft() when
implemented by the hardware.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20221221-wdat_wdt-timeleft-v1-1-8e8a314c36cc@weissschuh.net


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