msm: mdss: Fix potential deferencing of null pointer

While servicing display post processing ioctl for calib data the
driver checks if the calibration addr is valid. During this
check it deferences the base address for all pipes without
checking if the pipe pointer is NULL. This fix adds this check.

CRs-Fixed: 1082568
Change-Id: Id8164e3e9a6e5178d14dfce60eccbdb3f7a1b253
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>
Signed-off-by: Sachin Bhayare <sachin.bhayare@codeaurora.org>