Fix compile warnings in FramStorage

With some compilers we get warnings like this:

```console
Catena_FramStorage.h: In member function uint8_t McciCatena::cFramStorage::Object::setCurrent(uint8_t)
 
Catena_FramStorage.h: 357:3: warning: no return statement in function returning non-void [-Wreturn-type]
```

Problem is that `cFramStorage::setCurrent()` should be declared as `void`.