watchdog: renesas_wdt: stop when unregistering

We want to go into a sane state when unregistering. Currently, it
happens that the watchdog stops when unbinding because of RuntimePM
stopping the core clock. When rebinding, the core clock gets reactivated
and the watchdog fires even though it hasn't been opened by userspace
yet. Strange scenario, yes, but sane state is much preferred anyhow.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>