regulator: palmas: Return raw register values as the selectors in [get|set]_voltage_sel

Don't adjust the selector in [get|set]_voltage_sel, fix it in list_voltage() instead.

For smps*(except smps10), the vsel reg-value and voltage mapping as below:

reg-value       volt (uV) ( Assume RANGE is x1 )
0               0
1               500000
2               500000
3               500000
4               500000
5               500000
6               500000 (0.49V + 1 * 0.01V) * RANGE
7               510000 (0.49V + 2 * 0.01V) * RANGE
8               520000 (0.49V + 3 * 0.01V) * RANGE
9               530000 (0.49V + 4 * 0.01V) * RANGE
....

The linear mapping is start from selector 6.

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