regulator: tps6507x: Remove num_voltages array

We can get n_voltages for each regulator from table_len of struct tps_info.

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