docs: fix the incorrect group name of segment control

Summary:
Now the links in docs are connected normally.
related commit: https://phab.enlightenment.org/D7087

Test Plan: N/A

Reviewers: Jaehyun_Cho

Reviewed By: Jaehyun_Cho

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D7125

doc/index_elm.dox

@@ -204,7 +204,7 @@
  * @image html img/widget/radio/preview-00.png
  * @image latex img/widget/radio/preview-00.eps
  * @li @ref Elm_Route
- * @li @ref Elm_SegmentControl
+ * @li @ref Elm_Segment_Control
  *
  * @image html img/widget/segment_control/preview-00.png
  * @image latex img/widget/segment_control/preview-00.eps