drm/msm/sde: avoid null pointer dereference in secure_check

Add NULL pointer check while printing the crtc id during error
case. There is a possibility that the atomic state passed
might be NULL leading to cur_crtc not populated at all.

Change-Id: I49bef15ac0deeb6d731bffe7c9a0e8300b2c2fbb
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>