msm: vidc: Update encoder output size calculation

Based on discussion with firmware team change the bitstream
buffer size calculation for encoder. This logic is based on
experience from previous chipsets.

CRs-Fixed: 2368458
Change-Id: I5c351f6bfb53a4da492472993e5a9b6b8d5ad96e
Signed-off-by: Vaibhav Deshu Venkatesh <vdeshuve@codeaurora.org>