COMPMID-1246: Fix bug in handling backends that can't be loaded in the Graph API

Change-Id: Iefd175af2f472179d86df5358a1527a79c5666ed
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/145182
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Tested-by: Jenkins <bsgcomp@arm.com>
diff --git a/src/graph/backends/BackendRegistry.cpp b/src/graph/backends/BackendRegistry.cpp
index 2803322..dccfefc 100644
--- a/src/graph/backends/BackendRegistry.cpp
+++ b/src/graph/backends/BackendRegistry.cpp
@@ -48,6 +48,14 @@
     return _registered_backends[target].get();
 }
 
+IDeviceBackend &BackendRegistry::get_backend(Target target)
+{
+    IDeviceBackend *backend = find_backend(target);
+    ARM_COMPUTE_ERROR_ON_MSG(!backend, "Requested backend doesn't exist!");
+    ARM_COMPUTE_ERROR_ON_MSG(!backend->is_backend_supported(), "Requested backend isn't supported");
+    return *backend;
+}
+
 bool BackendRegistry::contains(Target target) const
 {
     auto it = _registered_backends.find(target);