efl_ui_radio: refactor for usage of efl_ui_check_selected

efl_ui_radio: refactor for usage of efl_ui_check_selected

in previous versions of this widget, the calls that are available due to
inheritance did not work. efl_ui_check_selected_set did not work on a
radio button. However, the internal function _state_set did just exactly
that. So this commit refactors the activity emitting out of the
function, so the _state_set function can just be used as the
efl_ui_check_selected set function.

Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Differential Revision: https://phab.enlightenment.org/D9059