avcodec/hevc: clear HEVClcList[i] on allocation

Fixes fate failure with --enable-memory-poisoning && make THREAD_TYPE=slice THREADS=7  fate-hevc-conformance-ENTP_C_Qualcomm_1

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
update for FFmpeg 2.3

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