mfd: max77686: Use NULL instead of 0

'data' is a pointer and hence use NULL instead of 0.
Silences the following warning:
drivers/mfd/max77686.c:49:50: warning: Using plain integer as NULL pointer
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Jonghwa Lee <jonghwa3.lee@samsung.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/max77686.c

@@ -46,7 +46,7 @@ static struct regmap_config max77686_regmap_config = {
 
 #ifdef CONFIG_OF
 static struct of_device_id max77686_pmic_dt_match[] = {
-	{.compatible = "maxim,max77686",        .data = 0},
+	{.compatible = "maxim,max77686", .data = NULL},
 	{},
 };