Don't list /lib/modules/$KernelVer/kernel twice
    
    For quite some time I see warnings like
        warning: File listed twice: /lib/modules/[...]/kernel
    
    when building the kernel-core rpm. This is because that directory is included
    both in module-dirs.list (and therefor in, basically, kernel-core.list) and in
    kernel_variant_files().
    
    Tweak the find command that generates module-dirs.list so that this directory
    is not included in that list anymore.
    
    Signed-off-by: Paul Bolle <pebolle@tiscali.nl>