msm: vidc: Re-use scratch buffer during port reconfig

During port reconfig, if new scratch buffer requirements
are satisfied by existing scratch buffers, then
driver should reuse the same buffers. By avoiding
free and re-allocation of buffers we will reduce
port reconfiguration latency.

Change-Id: Ice43d1c94a002e1f38b03f2c320ded5a47fd1ef7
Signed-off-by: Arun Menon <avmenon@codeaurora.org>