regulator: axp20x: Use regulator_map_voltage_ascend for LDO4

The voltages in axp20x_ldo4_data table are in ascendant order, so use
regulator_map_voltage_ascend.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/regulator/axp20x-regulator.c

@@ -111,6 +111,7 @@ static struct regulator_ops axp20x_ops_table = {
 	.set_voltage_sel	= regulator_set_voltage_sel_regmap,
 	.get_voltage_sel	= regulator_get_voltage_sel_regmap,
 	.list_voltage		= regulator_list_voltage_table,
+	.map_voltage		= regulator_map_voltage_ascend,
 	.enable			= regulator_enable_regmap,
 	.disable		= regulator_disable_regmap,
 	.is_enabled		= regulator_is_enabled_regmap,