msm: camera: sensor: Assign power settings pointer to null

Power settings pointers are assigned null after being freed.
This will make sure pointers do not point to some junk memory.

Change-Id: I85df098fc28f0afe9f765ddf7e22cc082e437753
Signed-off-by: Vishalsingh Hajeri <vhajeri@codeaurora.org>