msm: vidc: do not send release buffer to f/w in dynamic buffer mode

In dynamic buffer mode, the output buffers are not registered
with the firmware. So the v4l2 video driver does not need
to send release buffer command for output buffers to firmware.

Change-Id: I3b8f37fafe9fa07a45a68ded1de77e90f2764f6c
Signed-off-by: Arun Menon <avmenon@codeaurora.org>