[Tizen] Functions that return value types should not return them as const.

[Tizen] Functions that return value types should not return them as const.

It is ignored by the compiler and produces warnings.

- This patch is cherry-picked from devel/master branch.
  After DALi Integration (version up) to 1.2.23, this patch can be reverted.

Change-Id: I8f46f597718f72c15a4ca17f98751adf00057c20