kconfig: remove a spurious self-assignment

The self assignment was probably introduced by an automated code
refactoring in
commit 694c49a7 ("kconfig: drop localization support").

The issue was identified by a self-assign warning when running
make menuconfig with clang.

Fixes: 694c49a7

 ("kconfig: drop localization support")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>