avcodec/utils: correct align value for interplay

Fixes out of array access
Fixes: 452/fuzz-1-ffmpeg_VIDEO_AV_CODEC_ID_INTERPLAY_VIDEO_fuzzer

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
void av_register_hwaccel(AVHWAccel *hwaccel)
{
    AVHWAccel **p = last_hwaccel;
    hwaccel->next = NULL;
    while(*p || avpriv_atomic_ptr_cas((void * volatile *)p, NULL, hwaccel))
        p = &(*p)->next;
    last_hwaccel = &hwaccel->next;
}

void av_register_hwaccel(AVHWAccel *hwaccel)
{
    AVHWAccel **p = last_hwaccel;
    hwaccel->next = NULL;
    while(*p || avpriv_atomic_ptr_cas((void * volatile *)p, NULL, hwaccel))
        p = &(*p)->next;
    last_hwaccel = &hwaccel->next;
}
