Profiling on a Raspberry Pi revealed the best performance to correspond
with VLC_BITS = 5. Results for overall audio decode and the get_vlc2 function
in particular are as follows:

              Before          After
              Mean   StdDev   Mean   StdDev  Confidence  Change
6:2 total     348.8  20.1     339.6  15.1    88.8%       +2.7%  (insignificant)
6:2 function  38.1   8.1      26.4   4.1     100.0%      +44.5%
8:2 total     339.1  15.4     324.5  15.5    99.4%       +4.5%
8:2 function  33.8   7.0      27.3   5.6     99.7%       +23.6%
6:6 total     604.6  20.8     572.8  20.6    100.0%      +5.6%
6:6 function  95.8   8.4      68.9   8.2     100.0%      +39.1%
8:8 total     766.4  17.6     741.5  21.2    100.0%      +3.4%
8:8 function  106.0  11.4     86.1   9.9     100.0%      +23.1%
Signed-off-by: Martin Storsjö <martin@martin.st>