msm-camera: Validation of input parameter

The input array pointer cam_vreg and its associated length
num_vreg_seq is checked to avoid accessing the array if the
pointer is NULL and the associated length is non-zero. When
cam_vreg is NULL and num_vreg_seq is 0 the array does not
get accessed.

CRs-Fixed: 897259
Change-Id: I2f93955ec9a21c329290ead9706a7eeb1d640d3c
Signed-off-by: Trilokesh Rangam <tranga@codeaurora.org>