regulator: ab8500: Fix voltage_mask for AB8505_LDO_AUDIO

The voltage_mask and voltage_shift settings of AB8505_LDO_AUDIO are not matched.
It looks like a typo in the voltage_mask 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>