Sync backend only if allocated rather than supported

Resolve COMPMID-4785, COMPMID-4786, COMPMID-4787

Change-Id: Ic59463e69d824fa0db186f65c5108f18d99f4b73
Signed-off-by: Giorgio Arena <giorgio.arena@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/6165
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/src/graph/Utils.cpp b/src/graph/Utils.cpp
index ceb5ba9..7309737 100644
--- a/src/graph/Utils.cpp
+++ b/src/graph/Utils.cpp
@@ -120,7 +120,7 @@
 {
     for(const auto &backend : backends::BackendRegistry::get().backends())
     {
-        if(backend.second->is_backend_supported())
+        if(backend.second->backend_allocator())
         {
             backend.second->sync();
         }