regulator: isl6271a: Use NULL instead of 0

init_data is a pointer. Use NULL instead of 0.

Silences the following sparse warning:
drivers/regulator/isl6271a-regulator.c:133:44:
warning: Using plain integer as NULL pointer
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/isl6271a-regulator.c

@@ -130,7 +130,7 @@ static int isl6271a_probe(struct i2c_client *i2c,
 		if (i == 0)
 			config.init_data = init_data;
 		else
-			config.init_data = 0;
+			config.init_data = NULL;
 		config.driver_data = pmic;
 
 		pmic->rdev[i] = regulator_register(&isl_rd[i], &config);