msm: vidc: Deinit v4l2 control handler at the very end

Deinit v4l2 control handler after removing the instance
node from the core instance list. Without this change,
there could arise a situation where driver passes down
freed v4l2 control handler to v4l2 framework causing a
crash.

Change-Id: Icfafeb55eb6a4515cea5f8d5deb9503b90888f03
Signed-off-by: Arun Menon <avmenon@codeaurora.org>