mm-video: vidc: Flush m_input_free_q when input buffers are freed

Not flushing it can leave dangling pointers to old input buffers,
which get dereferenced if the component is re-used for another
session.
author:  Deva Ramasubramanian <dramasub@codeaurora.org>

bug: 10668205

Change-Id: I8356c7db9714d1c1d420d975aed0a7f50cdedef7