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>
diff --git a/drivers/mfd/max77686.c b/drivers/mfd/max77686.c
index 4d73963..1cbb176 100644
--- a/drivers/mfd/max77686.c
+++ b/drivers/mfd/max77686.c
@@ -46,7 +46,7 @@
 
 #ifdef CONFIG_OF
 static struct of_device_id max77686_pmic_dt_match[] = {
-	{.compatible = "maxim,max77686",        .data = 0},
+	{.compatible = "maxim,max77686", .data = NULL},
 	{},
 };