msm: vidc: Fixes bug in handling duplicate frames.

Fixes bug while closing encoder which supports
duplicate input frames. This fix decrements
the reference count of original frames
appropriately.

Change-Id: Ib542cf5fd790b8ba7f77e9a748a25c3cb132f40a
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>