watchdog: wdat_wdt: Stop watchdog when uninstalling module

Test shows that wachdog still reboots machine after the module
is removed. Use watchdog_stop_on_unregister to stop the watchdog
on removing.

Signed-off-by: Liu Xinpeng <liuxp11@chinatelecom.cn>
eviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1650984810-6247-4-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>