scripts: use CT_CONFIG_SHELL instead of CT_SHELL

CT_SHELL is undefined.
Thus, the generated wrapper scripts are not executable by the kernel
because they do not contain a valid interpreter.
Use CT_CONFIG_SHELL instead.

Signed-off-by: "Titus von Boxberg" <titus@v9g.de>
(transplanted from cf509170838f4e289fe25617e3f3db1d6d6ffc41)

menu "Debug facilities"

source "config.gen/debug.in"

endmenu