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)

 # Blackfin specific configuration file

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_DEFAULT_LE

 ## select ARCH_SUPPORT_ARCH

 ## select ARCH_SUPPORT_CPU

 ## select ARCH_SUPPORT_TUNE

 ## select ARCH_SUPPORT_FPU

 ##

 ## help The Blackfin architecture