elm_hoversel: change Elm_Hoversel_Data member name from scroll_enabled to scrollable

elm_hoversel: change Elm_Hoversel_Data member name from scroll_enabled to scrollable

Summary:
elm_hoversel_scroll_enabled_set/get() API were changed to
elm_hoversel_scrollable_set/get().
However, the name of member of Elm_Hovsersel_Data related to those API
are not changed.
It can confuse developers later, so change it same to the name defined
in elm_hoversel.eo file.

Reviewers: Hermet, cedric

Differential Revision: https://phab.enlightenment.org/D3140

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>