msm: camera: Added the NULL pointer check

Added the NULL pointer check for isp_config
to avoid the crashes

Change-Id: I2df7eeb5c633b04c3aac5d985cf50c2ece7f1076
CRs-Fixed: 495652
Signed-off-by: Ajay Dudani <adudani@codeaurora.org>

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>