watchdog: s3c2410_wdt: Remove unneeded initialization

Initializing clk to NULL as a reset/error condition does not
help as NULL is not an invalid condition w.r.t clk. Remove this
initialization altogether as there is no state retention.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>