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/MaximumTestImpl.cpp b/src/backends/backendsCommon/test/layerTests/MaximumTestImpl.cpp
index 07e2bef..0218697 100644
--- a/src/backends/backendsCommon/test/layerTests/MaximumTestImpl.cpp
+++ b/src/backends/backendsCommon/test/layerTests/MaximumTestImpl.cpp
@@ -19,6 +19,7 @@
 LayerTestResult<float, 4> MaximumSimpleTest(armnn::IWorkloadFactory& workloadFactory,
                                            const armnn::IBackendInternal::IMemoryManagerSharedPtr& memoryManager)
 {
+    boost::ignore_unused(memoryManager);
     const unsigned int width        = 2u;
     const unsigned int height       = 2u;
     const unsigned int channelCount = 2u;