msm: mdss: Add NULL pointer checks in mdss_mdp_wb_set_secure
msm: mdss: Add NULL pointer checks in mdss_mdp_wb_set_secure

Null pointer dereference can cause kernel panic, hence add
checks to avoid them.

CRs-Fixed: 553552
Change-Id: Ia854d7b65a5cf6a0fa214c34e658ea0f1380ac2c
Signed-off-by: Jayant Shekhar <86e2268d866be82fb5d37d90578bd70a827d7020@codeaurora.org>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas