One can offload the computation of the codes to
ff_init_vlc_from_lengths(); this also improves performance: The number
of decicycles for one call to read_code_table() decreased from 198343
to 148338 with the sample sample-cllc-rgb.avi from the FATE suite; it
has been looped 100 times and the test repeated ten times to test it
sufficiently often.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>