mfd: sec-core: Fix sparse NULL pointer warning

Fixes the following sparse warning:

drivers/mfd/sec-core.c:202:16: warning: Using plain integer as NULL pointer
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/sec-core.c

@@ -204,7 +204,7 @@ static struct sec_platform_data *sec_pmic_i2c_parse_dt_pdata(
 static struct sec_platform_data *sec_pmic_i2c_parse_dt_pdata(
 					struct device *dev)
 {
-	return 0;
+	return NULL;
 }
 #endif