hwc: Check for planeAlpha along with HWC_BLENDING_NONE

Check for planeAlpha along with HWC_BLENDING_NONE as the latter
is set if the layer is Opaque irrespective of planeAlpha value.

Change-Id: Iaee7efe662189ba3a2562f79c2d109da831ac94d
diff --git a/libhwcomposer/hwc_utils.cpp b/libhwcomposer/hwc_utils.cpp
index b091ae2..3732703 100644
--- a/libhwcomposer/hwc_utils.cpp
+++ b/libhwcomposer/hwc_utils.cpp
@@ -1382,7 +1382,8 @@
         //see if there is no blending required.
         //If it is opaque see if we can substract this region from below
         //layers.
-        if(list->hwLayers[i].blending == HWC_BLENDING_NONE) {
+        if(list->hwLayers[i].blending == HWC_BLENDING_NONE &&
+                list->hwLayers[i].planeAlpha == 0xFF) {
             int j= i-1;
             hwc_rect_t& topframe =
                 (hwc_rect_t&)list->hwLayers[i].displayFrame;