physical: Fix cppcoreguidelines-explicit-virtual-functions

```
/home/andrew/src/openbmc/phosphor-led-sysfs/build/../physical.hpp:32:5: error: annotate this function with 'override' or (rarely) 'final' [cppcoreguidelines-explicit-virtual-functions,modernize-use-override,-warnings-as-errors]
    ~Physical() = default;
    ^
                override
```

Change-Id: I0f631ec59c8b3035f085fe475465d4fb09183632
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
1 file changed