msm: vidc: vdec: recalculate input buffer count for HFR

Default buffer count will not be sufficient for HFR(fps > 480).
So recalculate buffer count, if fps is updated before calling
vidioc_reqbuf.

Change-Id: Iec792892d283072f064c4148c65560b6a7e31d45
Signed-off-by: Govindaraj Rajagopal <grajagop@codeaurora.org>