PEL: Add 'override' to derived destructors

cppcheck complains that it is overriding a virtual function in the base
class but isn't marked with override.

Change-Id: I4e03f0524987427e3742672d27b86c71943fab5b
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/extensions/openpower-pels/extended_user_header.hpp b/extensions/openpower-pels/extended_user_header.hpp
index 40da0b6..e964bd4 100644
--- a/extensions/openpower-pels/extended_user_header.hpp
+++ b/extensions/openpower-pels/extended_user_header.hpp
@@ -31,7 +31,7 @@
 {
   public:
     ExtendedUserHeader() = delete;
-    ~ExtendedUserHeader() = default;
+    ~ExtendedUserHeader() override = default;
     ExtendedUserHeader(const ExtendedUserHeader&) = default;
     ExtendedUserHeader& operator=(const ExtendedUserHeader&) = default;
     ExtendedUserHeader(ExtendedUserHeader&&) = default;