watchdog: mpc8xxx_wdt: Reload the watchdog timer when enabling the watchdog

[ Upstream commit 7dfd80f7 ]

When the watchdog gets enabled with this driver, it leaves enough time
for the core watchdog subsystem to start pinging it. But when the
watchdog is already started by hardware or by the boot loader, little
time remains before it fires and it happens that the core watchdog
subsystem doesn't have time to start pinging it.

Until commit 19ce9490 ("watchdog: mpc8xxx: use the core worker
function") pinging was managed by the driver itself and the watchdog
was immediately pinged by setting the timer expiry to 0.

So restore similar behaviour by pinging it when enabling it so that
if it was already enabled the watchdog timer counter is reloaded.

Fixes: 19ce9490 ("watchdog: mpc8xxx: use the core worker function")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>