hwc: Reset PTOR information

Reset PTOR info in HWC reset to make sure that Copybit does not draw
any Overlap region, even if there is no App layer in HWC layer list.

Change-Id: Ie2fb3408ba0171fd098a6b2627f4b9d59ae94ee6
diff --git a/libhwcomposer/hwc.cpp b/libhwcomposer/hwc.cpp
index 3026d99..5287377 100644
--- a/libhwcomposer/hwc.cpp
+++ b/libhwcomposer/hwc.cpp
@@ -222,6 +222,7 @@
             ctx->mLayerRotMap[i]->reset();
     }
 
+    memset(&(ctx->mPtorInfo), 0, sizeof(ctx->mPtorInfo));
     ctx->mAD->reset();
 
 }