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>
1 file changed