surfaceflinger: give hwcomposer a chance to release buffers

Change-Id: I605fa779702022865dd58df3b36f37c2644ade36
diff --git a/services/surfaceflinger/DisplayHardware/DisplayHardware.cpp b/services/surfaceflinger/DisplayHardware/DisplayHardware.cpp
index 166c528..3e23929 100644
--- a/services/surfaceflinger/DisplayHardware/DisplayHardware.cpp
+++ b/services/surfaceflinger/DisplayHardware/DisplayHardware.cpp
@@ -292,6 +292,9 @@
 void DisplayHardware::releaseScreen() const
 {
     DisplayHardwareBase::releaseScreen();
+    if (mHwc->initCheck() == NO_ERROR) {
+        mHwc->release();
+    }
 }
 
 void DisplayHardware::acquireScreen() const