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/journal.hpp b/extensions/openpower-pels/journal.hpp
index 620ce50..2707c44 100644
--- a/extensions/openpower-pels/journal.hpp
+++ b/extensions/openpower-pels/journal.hpp
@@ -48,7 +48,7 @@
 {
   public:
     Journal() = default;
-    ~Journal() = default;
+    ~Journal() override = default;
     Journal(const Journal&) = default;
     Journal& operator=(const Journal&) = default;
     Journal(Journal&&) = default;