get_bits: remove unused assignment

Bug-Id: CID 1238816
motion_est: remove dead code

mb_type is initialized to 0 and never updated before the check.

Bug-Id: CID 1238782
error_resilience: initialize prev_* variables

CC: libav-stable@libav.org
Bug-Id: CID 732293 / CID 732294
celp_filters: don't use filter lenght as loop bound

CC: libav-stable@libav.org
Bug-Id: CID 717906 / CID 717907 / CID 717916 /
        CID 717917 / CID 717919 / CID 732259
aacsbr: treat 1-d arrays as such

CC: libav-stable@libav.org
Bug-Id: CID 1238802 / CID 1238793 / CID 1238785
        CID 1238808 / CID 1238809
aacsbr: change order of operation to prevent out of array read

CC: libav-stable@libav.org
Bug-Id: CID 732250
aacdec: add default case in channel layout

Bug-Id: CID 732291