hqd: Fix validate and prepare frame for virtual displays

Extend validate and prepare frame functionality for
virtual displays.

Change-Id: I266f35d8581ac2de04c5ce22e51b267a48955e46
diff --git a/libhwcomposer/hwc_virtual.cpp b/libhwcomposer/hwc_virtual.cpp
index c081400..28dc991 100644
--- a/libhwcomposer/hwc_virtual.cpp
+++ b/libhwcomposer/hwc_virtual.cpp
@@ -122,7 +122,7 @@
 
         if(ctx->mMDPComp[dpy]->prepare(ctx, list) < 0) {
             const int fbZ = 0;
-            ctx->mFBUpdate[dpy]->prepare(ctx, list, fbZ);
+            ctx->mFBUpdate[dpy]->prepareAndValidate(ctx, list, fbZ);
         }
     }
     return 0;
@@ -213,7 +213,7 @@
             setListStats(ctx, list, dpy);
             if(ctx->mMDPComp[dpy]->prepare(ctx, list) < 0) {
                 const int fbZ = 0;
-                ctx->mFBUpdate[dpy]->prepare(ctx, list, fbZ);
+                ctx->mFBUpdate[dpy]->prepareAndValidate(ctx, list, fbZ);
             }
         } else {
             /* Virtual Display is in Pause state.