hwc : Fix crash during dumpsys

Dumpsys runs in different thread not in composition thread.
Accessing mdp composition frame info in dumpsys with out
synchronizing could cause crash since frame info can get reset
in composition thread.

CRs-fixed: 503268

Change-Id: If3f7d8cc9fce8b14622e666fa52583ff0cfdedd2
diff --git a/libhwcomposer/hwc_mdpcomp.h b/libhwcomposer/hwc_mdpcomp.h
index 6e04918..898771d 100644
--- a/libhwcomposer/hwc_mdpcomp.h
+++ b/libhwcomposer/hwc_mdpcomp.h
@@ -173,6 +173,7 @@
     static IdleInvalidator *idleInvalidator;
     struct FrameInfo mCurrentFrame;
     struct LayerCache mCachedFrame;
+    mutable Locker mMdpCompLock;
 };
 
 class MDPCompLowRes : public MDPComp {