msm: vidc: Amend input buffer count in batch mode

Batching needs minimum batch size count of input
buffers else we may not see expected power savings
in playback usecase.

Change-Id: I4355daadd0e416f4bd48103b59b44efccd2abe31
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>