Fix incorrect copyright notices

 * Updated headers that were missing a copyright notice.
 * Reverted years that were incorrectly updated.

Signed-off-by: Matthew Sloyan <matthew.sloyan@arm.com>
Change-Id: I65842f1e9b9fd5654563edd5090133cb3c89fecc
diff --git a/src/armnnDeserializer/test/DeserializeReduceSum.cpp b/src/armnnDeserializer/test/DeserializeReduceSum.cpp
index 1d72b0f..0405b0e 100644
--- a/src/armnnDeserializer/test/DeserializeReduceSum.cpp
+++ b/src/armnnDeserializer/test/DeserializeReduceSum.cpp
@@ -1,5 +1,6 @@
 //
 // Copyright © 2020 Samsung Electronics Co Ltd and Contributors. All rights reserved.
+// Copyright © 2021 Arm Ltd and Contributors. All rights reserved.
 // SPDX-License-Identifier: MIT
 //