msm: vidc: Increase min input buffer count by 2

This smoothens the buffer flow and takes care of random
frame drops due to jitter.

CRs-Fixed: 2478892
Change-Id: I27ecb686e3982152b18f3a2fc207ecf59f928dff
Signed-off-by: Chinmay Sawarkar <chinmays@codeaurora.org>