hwc: Silence log for unsupported layers

In some cases, external displays may be driven by the primary
vsync with the primary not having any layers to compose. Do not
log in such cases.

Bug: 23487270
Change-Id: If72cb690692faa26bb4132c0f473b8b413be2bee
diff --git a/msm8994/libhwcomposer/hwc_mdpcomp.cpp b/msm8994/libhwcomposer/hwc_mdpcomp.cpp
index 2b5c29b..4c7c7ad 100644
--- a/msm8994/libhwcomposer/hwc_mdpcomp.cpp
+++ b/msm8994/libhwcomposer/hwc_mdpcomp.cpp
@@ -2015,8 +2015,8 @@
 
     //Do not cache the information for next draw cycle.
     if(numLayers > MAX_NUM_APP_LAYERS or (!numLayers)) {
-        ALOGI("%s: Unsupported layer count for mdp composition",
-                __FUNCTION__);
+        ALOGI_IF(numLayers, "%s: Unsupported layer count for mdp composition: %d",
+                __FUNCTION__, numLayers);
         mCachedFrame.reset();
 #ifdef DYNAMIC_FPS
         // Reset refresh rate