msm: camera: sensor: Correct power down operation in shutdown

Currently release dev ioctl call is doing sensor power down, and as
a part of this operation regulator handle is been released. Shutdown
call after release should not call for the sensor power down. This
change adds necessary condition check for sensor power down operation
for the shutdown operation.

Change-Id: Ia5547a71f43af4c0b1641aa46606bbef0516b980
Signed-off-by: Jigarkumar Zala <jzala@codeaurora.org>