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/joystick12/joystick12.hpp

@@ -52,7 +52,7 @@ namespace upm {
  * 2-axis analog joystick.
  *
  * @image html joystick12.jpg
- * @snippet joystick12-example.cxx Interesting
+ * @snippet joystick12.cxx Interesting
  */
 class Joystick12 {
     public: