regulator: ab8500: Fix list_voltage for fixed voltage regulators

commit b080c78a4e447e9c212c207f725999d4e32c5f19
"regulator: ab8500: Update voltage handling for fixed voltage regulators"
removes min_uV settings and sets volt_table for all fixed voltages, thus
we can not use regulator_list_voltage_linear now. Use
regulator_list_voltage_table instead.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>