IVGCVSW-1985: Replace std::string* reasonIfNotSupported with Optional<std::string&> in IsLayerSupported implementations

Change-Id: I2f054f0dcff9bdc86ee90c55b3e94c6b4ae25085
diff --git a/src/backends/cl/workloads/ClPadWorkload.cpp b/src/backends/cl/workloads/ClPadWorkload.cpp
index 45dc5e8..89b0d8f 100644
--- a/src/backends/cl/workloads/ClPadWorkload.cpp
+++ b/src/backends/cl/workloads/ClPadWorkload.cpp
@@ -35,10 +35,9 @@
     m_Layer.run();
 }
 
-bool ClPadValidate(const TensorInfo& input,
-                   const TensorInfo& output,
-                   const PadDescriptor& descriptor,
-                   std::string* reasonIfUnsupported)
+arm_compute::Status ClPadValidate(const TensorInfo& input,
+                                  const TensorInfo& output,
+                                  const PadDescriptor& descriptor)
 {
     const arm_compute::TensorInfo aclInputInfo = BuildArmComputeTensorInfo(input);
     const arm_compute::TensorInfo aclOutputInfo = BuildArmComputeTensorInfo(output);
@@ -48,13 +47,7 @@
                                                                             &aclOutputInfo,
                                                                             padList);
 
-    const bool supported = (aclStatus.error_code() == arm_compute::ErrorCode::OK);
-    if (!supported && reasonIfUnsupported)
-    {
-        *reasonIfUnsupported = aclStatus.error_description();
-    }
-
-    return supported;
+    return aclStatus;
 }
 
 } // namespace armnn