watchdog: gpio-wdt: ping already at startup for always running devices

During probe for an always-running watchdog a timer is setup to
constantly ping the watchdog while the device is not open. The gpio to
ping the watchdog is setup to inactive.

For a watchdog with hw_algo = "toggle" this results in a ping depending
on the initial state of the gpio, for hw_algo = "level" no ping is
generated.

Make sure that the first automatic ping is sent immediately and not only
when the timer expires the first time. This makes the machine survive in
case more than half of the watchdog timeout is already elapsed. (Which
is very probable for the chip I'm faced with that has a timeout of one
second.)

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>