Camera: synchronize mOutputStreams access

mOutputStreams access used to be protected by mLock, but that has
changed due to:
   - Treble interface switched from passing stream pointer to
     stream index
   - The buffer management API runs in HAL callback thread

Test: CTS
Bug: 109829698
Change-Id: I3561b197f46f07d2a15bb4f52b096f36c73a0407
2 files changed