msm:vidc: Fix buffer pool index

While searching for the available buffer entry
in the buffer pool the search should begin from
index 1 as zeroth entry is reserved.

CRs-fixed: 366361
Change-Id: I051b0232bb782f073ba9ad0b757a799703814df3
Signed-off-by: Mohan Kumar Gubbihalli Lachma Naik <mgubbi@codeaurora.org>