sysfs: Fix cppcoreguidelines-special-member-functions

```
../sysfs.hpp:24:7: error: class 'SysfsLed' defines a default destructor and a copy constructor but does not define a copy assignment operator, a move constructor or a move assignment operator [cppcoreguidelines-special-member-functions,-warnings-as-errors]
class SysfsLed
      ^
```

Change-Id: I778766f6285e87f6c3de194e058ecf6e620e4512
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
1 file changed