If the watchdog control register indicates that the watchdog hardware
is disabled even after we tried to enable it, there is no point to
instantiate the driver.

Cc: Zoltán Böszörményi <zboszor@pr.hu>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>