efl_ui_exact_model: use eina APIs to get the nth data
Summary:
Also, fixes a compiler warning
../src/lib/elementary/efl_ui_exact_model.c:60:17: warning: variable 'tbuf' set but not used [-Wunused-but-set-variable]
Test Plan: ninja
Reviewers: cedric, zmike, bu5hm4n
Reviewed By: zmike
Subscribers: reviewers, committers
Tags: efl
Differential Revision: https://phab.enlightenment.org/D11380