regulator: isl6271a: Remove setting map_voltage callback for isl_fixed_ops

isl_fixed_ops does not implement set_voltage_sel callback, adding map_voltage
here is misleading.
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/isl6271a-regulator.c

@@ -81,7 +81,6 @@ static int isl6271a_get_fixed_voltage(struct regulator_dev *dev)
 static struct regulator_ops isl_fixed_ops = {
 	.get_voltage	= isl6271a_get_fixed_voltage,
 	.list_voltage	= regulator_list_voltage_linear,
-	.map_voltage	= regulator_map_voltage_linear,
 };
 
 static const struct regulator_desc isl_rd[] = {