ls: code shrink

ls: code shrink

function                                             old     new   delta
count_dirs                                            81      86      +5
dnalloc                                               13      17      +4
showfiles                                            372     370      -2
ls_main                                              833     825      -8
showdirs                                             505     489     -16
splitdnarray                                         189     120     -69
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/4 up/down: 9/-95)             Total: -86 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>