msm: vidc: amend DCVS buffer count logic

The current DCVS buffer count logic results in zero
buffer count ourside the firmware initially which is
wrong as all the buffers are with client initially.
In some video usecases the buffer count outside the
firmware is never reaching to max threshold number
and driver end up setting increased clock rate always.
To avoid over voting, count the buffers queued to the
firmware (instead of counting buffers outside firmware)
which is acurate from the beginning.

Change-Id: I7a5cd7fddc88ddd96fb1db30c003501938f1a05a
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>