msm: vidc: Honor client's request for more buffers

The driver should allow the client's request for more buffers than the
minimum rather than enforcing just the minimum required by Venus.

Change-Id: I8c10372b1ffef55d0e73b824b13ad80de2446f23
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>