watchdog: s3c2410: Remove confusing CONFIG prefix from local defines

The CONFIG prefix from defines in the s3c2410_wdt.c might suggest that
these constants come from Kconfig.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>