msm: vidc: flush dynamic output buffers in reconfig

In dynamic buffer mode, if driver receives a
flush during reconfig, it should release all
buffers held in the kernel and not queued to
firmware. Without this change, the buffers held in
the kernel do not get flushed and video client
hangs waiting for release of output buffer.

Change-Id: I39bc31bda755947dec0db8a55583da8ad5b21678
Signed-off-by: Arun Menon <avmenon@codeaurora.org>