build/menuconfig: fix kconfig_edit

This fixes regression from commits 0431a519 and b4c30197.

pmbootstrap kconfig_edit raised an error while trying to checksum a package.

Error was:

(028793) [16:13:22] ERROR: 'module' object is not callable
(028793) [16:13:22] See also: <https://postmarketos.org/troubleshooting>
(028793) [16:13:22] Traceback (most recent call last):
    File "/home/lexx/dev/pmos/pmbootstrap/pmb/__init__.py", line 63, in main
    getattr(frontend, args.action)(args)
    File "/home/lexx/dev/pmos/pmbootstrap/pmb/helpers/frontend.py", line 279, in kconfig
    pmb.build.menuconfig(args, args.package)
    File "/home/lexx/dev/pmos/pmbootstrap/pmb/build/menuconfig.py", line 158, in menuconfig
    pmb.build.checksum(args, pkgname)
TypeError: 'module' object is not callable

The function was renamed, call new function.