msm: camera: Optimize the live snapshot state machine

Send the ack for live snapshot done event once its
completed instead of waiting for stop request from
user. This helps in saving a wait time which could
be upto 2 frame time in worst case

Change-Id: Ibbef211512e4b9f06ff6b8d3ca52d1dc591c0b46
Signed-off-by: Nishant Pandit <npandit@codeaurora.org>