watchdog: use dev_ functions

While they are registered all our watchdogs now have a valid device object
so we can in turn use that to report problems nicely.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>