msm: vidc: Fix concurrency issues in bus voting

when concurrent sessions are running, vote data of current
instance is getting reset due to next subsequent call.
Avoid sharing common vote data structure to avoid race-condition.

Change-Id: Ie188edf2619dc8f26a4d43093fd0cda4d4113737
Signed-off-by: Mahesh Voorugonda <mvooru@codeaurora.org>