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/src.hpp b/extensions/openpower-pels/src.hpp
index fa3a952..781274e 100644
--- a/extensions/openpower-pels/src.hpp
+++ b/extensions/openpower-pels/src.hpp
@@ -71,7 +71,7 @@
     };
 
     SRC() = delete;
-    ~SRC() = default;
+    ~SRC() override = default;
     SRC(const SRC&) = delete;
     SRC& operator=(const SRC&) = delete;
     SRC(SRC&&) = delete;