[WATCHDOG] sc1200wdt.c pnp unregister fix.

If no devices found or invalid parameter is specified,
scl200wdt_pnp_driver is left unregistered.
It breaks global list of pnp drivers.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>