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/pldm_interface.hpp b/extensions/openpower-pels/pldm_interface.hpp
index 30ff749..c350ede 100644
--- a/extensions/openpower-pels/pldm_interface.hpp
+++ b/extensions/openpower-pels/pldm_interface.hpp
@@ -54,7 +54,7 @@
     /**
      * @brief Destructor
      */
-    ~PLDMInterface();
+    ~PLDMInterface() override;
 
     /**
      * @brief Kicks off the send of the 'new file available' command