stagefright: reuse buffers instead of cloning

In buffer array mode, the buffer reference is kept in clients of
MediaCodec, so allocating new buffer for new input/output does not
work in that case.

Bug: 32577275
Bug: 32579231
Test: use screenrecord and investigate the output file.
Test: cts-tradefed run cts-dev -m CtsMediaTestCases -t android.media.cts.EncodeDecodeTest
Change-Id: I26d89f6b5735094062b8a2027bcab4754576d574