sc1200_wdt: Fix oops

If loaded with isapnp = 0 the driver explodes. This is catching
people out now and then. What should happen in the working case is
a complete mystery and the code appears terminally confused, but we
can at least make the error path work properly.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Partially-Resolves-bug: https://bugzilla.kernel.org/show_bug.cgi?id=53991