TAS2770 fixes

TAS2770 fixes

Merge series from Martin Povišer <povik+lin@cutebit.org>:

The first two fixes should be straightforward.

The latter two clean up what looks to me like a mess in the setting of
power levels. However we settle it, we should then do the same changes
to TAS2764, which has the same template (and maybe there are other
drivers).