hwc: fixed layers can't draw with gpu in time.

Func rcPostAllLayersDone only encode control data to buffer in stream,
but not send to anbox with pipe in time, which is done by flush() func.

android/hwcomposer/hwcomposer.cpp

@@ -210,6 +210,7 @@ static int hwc_set(hwc_composer_device_1_t* dev, size_t numDisplays,
     }
 
     rcEnc->rcPostAllLayersDone(rcEnc);
+    hostCon->flush();
 
     check_sync_fds(numDisplays, displays);