regulator: max8997: Remove n_bits from struct voltage_map_desc

regulator: max8997: Remove n_bits from struct voltage_map_desc

The n_bits is only used in max8997_get_voltage_proper_val to check the valid
range for variable i.

Current code already ensures min_vol never greater than desc->max,
which means the variable i always in the valid range:
0 .. (desc->max - desc->min)/desc->step.

Thus we can remove the checking (i >= (1 << desc->n_bits) and then remove
n_bits from struct voltage_map_desc.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>