msm: vidc: Validate userspace buffer count

Makesure the number of buffers count is less than
the maximum limit to avoid structure overflow errors.

Change-Id: Icf3850de36325637ae43ac95f1c8f0f63e201d31
CRs-fixed: 563694
Signed-off-by: Pachika, Vikas Reddy <vpachi@codeaurora.org>