Fixes tsan warnings in several audio codecs (flac, alac, wavpack, tta
and tak) that look like this:

WARNING: ThreadSanitizer: data race (pid=14340)
  Read of size 4 at 0x7d64000169d8 by main thread (mutexes: write M1335):
    #0 update_context_from_thread src/libavcodec/pthread_frame.c:284 (ffmpeg+0x000000dc795f)
[..]
  Previous write of size 4 at 0x7d64000169d8 by thread T1 (mutexes: write M1333):
    #0 wavpack_decode_block src/libavcodec/wavpack.c:1012 (ffmpeg+0x00000112b175)