msm: mdss: Fix NULL pointer dereference in mdss_mdp_display_wait4comp
msm: mdss: Fix NULL pointer dereference in mdss_mdp_display_wait4comp

Add sanity check for ctl to prevent NULL pointer dereference
leading to kernel panic.

CRs-Fixed: 578595
Change-Id: Iace727501856d9f93ba87eca92f9f000c32d2c8f
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