hwc2: Add HIDL callback to getDisplayAttributes()

Change-Id: Ic61111f8c6531a086dbd0f27adcd5c0691da267e
diff --git a/sdm/libs/hwc2/hwc_session_services.cpp b/sdm/libs/hwc2/hwc_session_services.cpp
index f4241e0..6550101 100644
--- a/sdm/libs/hwc2/hwc_session_services.cpp
+++ b/sdm/libs/hwc2/hwc_session_services.cpp
@@ -251,6 +251,7 @@
       }
     }
   }
+  _hidl_cb(error, display_attributes);
 
   return Void();
 }