list/genlist/gengrid: Fix default return value in eolian APIs.

list/genlist/gengrid: Fix default return value in eolian APIs.

Summary:
Some APIs need to return specific values for their usage.
For Examples, elm_xx_select_mode_get function need to return
ELM_OBJECT_SELECT_MODE_MAX when invalid input comes.
**Fixed API list :**
elm_list_mode_get
elm_list_multi_select_mode_get
elm_genlist_mode_get
elm_genlist_select_mode_get
elm_genlist_multi_select_mode_get
elm_genlist_item_type_get
elm_genlist_ttem_index_get
elm_genlist_item_select_mode_get
elm_gengrid_select_mode_get
elm_gengrid_multi_select_mode_get
elm_gengrid_item_index_get

Test Plan: Call API with NULL parameter and check return value.

Reviewers: Hermet, seoz, jaehwan, raster, eunue

Subscribers: id213sin

Differential Revision: https://phab.enlightenment.org/D2306