msm-camera: fix issue of isp unlock method

When we invoke isp unlock, it means isp hardware update is just
finished, we should update the "last update frame index" with
current frame id, so that the second hardware update can be avoided
in this frame.

Change-Id: Ib1f9458cba5c93f8d81b8f483f061747450ec3fd
Signed-off-by: ksui <ksui@codeaurora.org>