regulator: ab8500: Remove set_voltage_time_sel and delay setting

The data sheet does not specify time delay for voltage selection,
thus remove set_voltage_time_sel and delay setting.

Note, currently set_voltage_time_sel callback returns 0 due to missing
delay settings.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Bengt Jonsson <bengt.g.jonsson@stericsson.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>