msm: vidc: Increase maximum buffer count limit

Some clients want to allocate more buffers on decoder
input port than required (mainly for performance reasons).
Video decoder should honor the client request as long as
V4L2 framework permits.

CRs-fixed: 509088
Change-Id: Ic0da1b11ca49ebcd4498f8c8d93ba5b0e2dae8ba
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>