sssctl: Fix warning may be used uninitialized
    
    gcc 7 probably does some new optimisations which might cause few
    wariables to be uninitialized.
    
    src/tools/sssctl/sssctl_cache.c: In function ‘sssctl_print_object’:
    src/tools/sssctl/sssctl_cache.c:523:13: error: ‘dom’ may be used uninitialized
      in this function [-Werror=maybe-uninitialized]
             ret = info[i].attr_fn(tmp_ctx, entry, dom, info[i].attr, &value);
             ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    src/tools/sssctl/sssctl_cache.c:472:15: error: ‘entry’ may be used
      uninitialized in this function [-Werror=maybe-uninitialized]
         *_entry = talloc_steal(mem_ctx, entry);
                   ^~~~~~~~~~~~
    src/tools/sssctl/sssctl_cache.c:437:25: note: ‘entry’ was declared here
         struct sysdb_attrs *entry;
                             ^~~~~
    
    Another workaround would be to remove static modifier from function
    sssctl_find_object which probably prevents some inlinig + optimisation.
    
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>