msm: camera: Free power setting pointer during shutdown

Free power up and power down setting pointers during
power down of sensor modules. Also, add check to avoid
memory allocation in multiple calls.

Change-Id: I469453af060fb832e1b6e286fdb3c2954f6c9fe4
Signed-off-by: Ravi Kishore Tanuku <rktanuku@codeaurora.org>