display: remove compiler warnings

Use correct typecasts and format specifiers and resolve
compiler warnings

Change-Id: I51b12ecb78a9a496cf1f76c3d32892a203f70c43
diff --git a/libhwcomposer/hwc_mdpcomp.cpp b/libhwcomposer/hwc_mdpcomp.cpp
index b0953da..7c29502 100644
--- a/libhwcomposer/hwc_mdpcomp.cpp
+++ b/libhwcomposer/hwc_mdpcomp.cpp
@@ -1682,6 +1682,8 @@
     //fbz is above 4k2k layer, increment fb zorder by 1
     //as we split 4k2k layer and increment zorder for right half
     //of the layer
+    if(!ctx)
+        return;
     if(mCurrentFrame.fbZ >= 0) {
         for (int index = 0, mdpNextZOrder = 0; index < mCurrentFrame.layerCount;
                 index++) {