efl_ui_bg: fix unclipped image on EFL_UI_IMAGE_SCALE_TYPE_NONE

efl_ui_bg: fix unclipped image on EFL_UI_IMAGE_SCALE_TYPE_NONE

@fix

Summary:
efl_ui_bg has internal image and image may be larger than
         resize_obj when EFL.UI.IMAGE.SCALE_TYPE is none.
         Now resize_obj clips the internal image.

Test Plan:
1.Run elementary_test, part background(will be added soon)
2.Create a bg in a box with other widgets.
  Set bg as EFL_UI_IMAGE_SCALYE_TYPE_NONE.

Reviewers: jpeg, cedric

Reviewed By: cedric

Subscribers: woohyun

Differential Revision: https://phab.enlightenment.org/D5509

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