regulator: 88pm8607 - fix value range checking for accessing info->vol_table

In choose_voltage(), we use i as array index of info->vol_table.
The valid value range for i should be 0 .. ARRAY_SIZE(info->vol_table) - 1.

Take LDO1 as example, ARRAY_SIZE(LDO1_table) is 4, vol_nbits of LDO1 is 2.
for (i = 0; i < (2 << info->vol_nbits); i++)  is equivalent to
for (i = 0; i < 8; i++)
which is wrong.

The same value range checking also applies for index in pm8607_list_voltage().

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Mark Brown <broonie@openource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>