SF: replicate mSidebandStream in LayerBE

Add a copy of mSidebandStream in LayerBE.  This is
one of the few data items that is replicated in
both FE and BE.

Test: build
Change-Id: Ief98645a4fa178e2606c0c337b3f260a1766597a
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index e29132d..f4eace8 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -1002,7 +1002,7 @@
     const bool resizePending = ((c.requested.w != c.active.w) || (c.requested.h != c.active.h)) &&
             (mActiveBuffer != nullptr);
     if (!isFixedSize()) {
-        if (resizePending && mSidebandStream == NULL) {
+        if (resizePending && getBE().mSidebandStream == NULL) {
             flags |= eDontUpdateGeometryState;
         }
     }