kbuild: Fix LOADLIBES rename in Documentation/kbuild/makefiles.txt

Fixes: 8377bd2b ("kbuild: Rename HOST_LOADLIBES to KBUILD_HOSTLDLIBS")
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Acked-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>