msm: vidc: fix a race condition in cluster construction

At start of video session, when the super cluster is
constructed, it refers to a global static variable.
If we have multiple instances running simultaneously,
there exists a race condition, causing the instance
to register wrong cluster. Later on when a control
gets set in encoder, if the control is not found in
the cluster, we hit a BUG_ON, crashing the device.

Change-Id: Ib4ee64d684d903bb4f22310a1b34619728405649
Signed-off-by: Arun Menon <avmenon@codeaurora.org>