regulator: lp8755: Provide map_voltage()

Improve performance when setting voltages by avoiding a scan through the
selectors when we can simply calculate the selector we want.

Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/regulator/lp8755.c

@@ -229,6 +229,7 @@ err_i2c:
 }
 
 static struct regulator_ops lp8755_buck_ops = {
+	.map_voltage = regulator_map_voltage_linear,
 	.list_voltage = regulator_list_voltage_linear,
 	.set_voltage_sel = regulator_set_voltage_sel_regmap,
 	.get_voltage_sel = regulator_get_voltage_sel_regmap,