kconfig: gconf: fix single view to display dependent symbols correctly

In the following example, the symbol C was never displayed in Single
view. Fix the recursion logic so that all symbols are shown.

  menu "menu"

  config A
          bool "A"

  config B
          bool "B"
          depends on A

  config C
          bool "C"
          depends on B

  endmenu

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>