IVGCVSW-4246 Clean build of LayerTests with -Wextra

Change-Id: If3d98e45a6e2fa8e1afd19a4052334335feacf63
Signed-off-by: Derek Lamberti <derek.lamberti@arm.com>
diff --git a/src/backends/backendsCommon/test/layerTests/ConvertFp32ToFp16TestImpl.cpp b/src/backends/backendsCommon/test/layerTests/ConvertFp32ToFp16TestImpl.cpp
index e5184e0..f758f4b 100644
--- a/src/backends/backendsCommon/test/layerTests/ConvertFp32ToFp16TestImpl.cpp
+++ b/src/backends/backendsCommon/test/layerTests/ConvertFp32ToFp16TestImpl.cpp
@@ -16,6 +16,7 @@
     armnn::IWorkloadFactory& workloadFactory,
     const armnn::IBackendInternal::IMemoryManagerSharedPtr& memoryManager)
 {
+    boost::ignore_unused(memoryManager);
     using namespace half_float::literal;
 
     const armnn::TensorInfo inputTensorInfo({1, 3, 2, 3}, armnn::DataType::Float32);