msm: cvp: Ensure validity of shared HFI queue indices

CVP driver and CVP firmware communicates over shared
HFI queues. The queue header has the indices which synchronizes
the read and write between the driver and firmware. The change
ensures that the indices are within the valid range before
accessing them.

Change-Id: I729063aa6f2b8be1c4dffc817e0503d31ab8f961
Signed-off-by: George Shen <sqiao@codeaurora.org>