msm: vidc: Modify DCVS scaling window

DCVS scaling window should be equal to the additional buffers
allocated for DCVS and independent of the buffer count required
by Client and FW.

CRs-Fixed: 2527739
Change-Id: I665a3d9792f44ea031d6c8d05d6e7a546a22f9a8
Signed-off-by: Chinmay Sawarkar <chinmays@codeaurora.org>