ls: code shrink

ls: code shrink

function                                             old     new   delta
sort_and_display_files                                 -     427    +427
scan_and_display_dirs_recur                          497     488      -9
ls_main                                              765     735     -30
display_files                                        422       -    -422
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 0/2 up/down: 427/-461)          Total: -34 bytes

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