cllc: Pad swapped buffer

The bitstream buffer must be padded, or the bitstream reader might
read over the end.

Fixes the following valgrind warning:
    Use of uninitialised value of size 8 at 0x591BAE: cllc_decode_frame (cllc.c:166)

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
