elm_multibuttonentry: send "clicked" signal when item got hardware enter key.

elm_multibuttonentry: send "clicked" signal when item got hardware enter key.

Summary:
It was kind of bug state before.

There was no any action when the user gives a focus on an item. then press the enter key.
The item should be set as selected state after that should call clicked signal.

@fix

Test Plan: elementary test MBE sample.

Reviewers: woohyun, bu5hm4n, Hermet

Subscribers: cedric, jpeg

Differential Revision: https://phab.enlightenment.org/D4368

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