watchdog: wdat_wdt: Using the existing function to check parameter timeout

If max_hw_heartbeat_ms is provided, the configured maximum timeout is not
limited by it. The limit check in this driver therefore doesn't make much
sense. Similar, the watchdog core ensures that minimum timeout limits are
met if min_hw_heartbeat_ms is set. Using watchdog_timeout_invalid() makes
more sense because it takes this into account.

Signed-off-by: Liu Xinpeng <liuxp11@chinatelecom.cn>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1650984810-6247-2-git-send-email-liuxp11@chinatelecom.cn
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>