[sf] fix snapshot updates for mirror layers

Ensure we update the mirrored snapshots when they are
created.

Test: atest CtsSurfaceControlTests
Bug: 238781169

Change-Id: I245702f8b521745ba59f0f993bcaef90d0cdbe9a
diff --git a/services/surfaceflinger/FrontEnd/LayerHierarchy.cpp b/services/surfaceflinger/FrontEnd/LayerHierarchy.cpp
index afe557e..14d67c6 100644
--- a/services/surfaceflinger/FrontEnd/LayerHierarchy.cpp
+++ b/services/surfaceflinger/FrontEnd/LayerHierarchy.cpp
@@ -449,7 +449,7 @@
     traversalPath.id = layerId;
     traversalPath.variant = variant;
     if (variant == LayerHierarchy::Variant::Mirror) {
-        traversalPath.mirrorRootId = layerId;
+        traversalPath.mirrorRootId = mParentPath.id;
     } else if (variant == LayerHierarchy::Variant::Relative) {
         if (std::find(traversalPath.relativeRootIds.begin(), traversalPath.relativeRootIds.end(),
                       layerId) != traversalPath.relativeRootIds.end()) {