hwc: User Layercache for external display

Change-Id: Ibca92e1470ef72dc02d16d4ef8c05f1a1d2d485c
diff --git a/libhwcomposer/hwc.cpp b/libhwcomposer/hwc.cpp
index 23ffa42..f21d449 100644
--- a/libhwcomposer/hwc.cpp
+++ b/libhwcomposer/hwc.cpp
@@ -127,7 +127,7 @@
             if(!MDPComp::configure(ctx, list)) {
                 VideoOverlay::prepare(ctx, list, HWC_DISPLAY_PRIMARY);
                 FBUpdate::prepare(ctx, fbLayer, HWC_DISPLAY_PRIMARY);
-                ctx->mLayerCache->updateLayerCache(list);
+                ctx->mLayerCache[HWC_DISPLAY_PRIMARY]->updateLayerCache(list);
             }
         }
     }
@@ -150,6 +150,7 @@
 
             VideoOverlay::prepare(ctx, list, HWC_DISPLAY_EXTERNAL);
             FBUpdate::prepare(ctx, fbLayer, HWC_DISPLAY_EXTERNAL);
+            ctx->mLayerCache[HWC_DISPLAY_EXTERNAL]->updateLayerCache(list);
         }
     }
     return 0;