kconfig: qconf: simplify the goBack() logic

The goBack() logic is used only for the configList, as
it only makes sense on singleMode. So, let's simplify the
code.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>