msm-camera: Assign NULL after freeing memory

In msm_actuator we need to assign memory
pointer to  NULL after freeing that memory
using kfree.

CRs-Fixed: 621818

Change-Id: I54a9b9a2ff913a795c0089c996a8415c64bdd5d5
Signed-off-by: Raghu DP <dp.raghu@codeaurora.org>