IVGCVSW-4246 Clean build of backends with -Wextra

Change-Id: I9e8d5576b3ec04c871785d5f2f9545bf1136e59b
Signed-off-by: Derek Lamberti <derek.lamberti@arm.com>
diff --git a/include/armnn/backends/IBackendInternal.hpp b/include/armnn/backends/IBackendInternal.hpp
index 3296d81..3533ace 100644
--- a/include/armnn/backends/IBackendInternal.hpp
+++ b/include/armnn/backends/IBackendInternal.hpp
@@ -127,7 +127,7 @@
     /// (Optional) Register TensorHandleFactories
     /// Either this method or CreateMemoryManager() and
     /// IWorkloadFactory::CreateTensor()/IWorkloadFactory::CreateSubtensor() methods must be implemented.
-    virtual void RegisterTensorHandleFactories(class TensorHandleFactoryRegistry& registry) {}
+    virtual void RegisterTensorHandleFactories(class TensorHandleFactoryRegistry& /*registry*/) {}
 
     /// Returns the version of the Backend API
     static constexpr BackendVersion GetApiVersion() { return BackendVersion(1, 0); }