IVGCVSW-7024 Add missing license info for reuse lint

Signed-off-by: Jim Flynn <jim.flynn@arm.com>
Change-Id: I97dee6982e0a7be01c13e9e803c0997547a39ff1
diff --git a/third-party/fmt/format.h b/third-party/fmt/format.h
index 712c6eb..20ed0bb 100644
--- a/third-party/fmt/format.h
+++ b/third-party/fmt/format.h
@@ -3,6 +3,8 @@
 
  Copyright (c) 2012 - present, Victor Zverovich
 
+ SPDX-License-Identifier: MIT
+
  Permission is hereby granted, free of charge, to any person obtaining
  a copy of this software and associated documentation files (the
  "Software"), to deal in the Software without restriction, including