snippet: Updated all snippet tags

Ensure all src C++ headers which have corresponding C++ examples have
doxygen tags which point to those examples.  Some were missing, some
were invalid, some needed to be updated to match the new example names.

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/gas/tp401.hpp

@@ -50,7 +50,7 @@ namespace upm {
    * operation to stabilize completely.
    *
    * @image html tp401.jpeg
-   * @snippet tp401.cxx Interesting
+   * @snippet gas-tp401.cxx Interesting
    */
     class TP401 : public Gas {
         public: