alacenc: fix incorrect buffer use

The issue lies in actually dead code ("for now it's not used").

Noticed-by: Justin Ruggles
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
alacenc: remove unneeded masking

The extra bits have already been masked, so this was not doing anything.

Noticed-by: Justin Ruggles
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>