fsck: use getmntent_r instead of open-coded parsing. By Vladimir

fsck: use getmntent_r instead of open-coded parsing. By Vladimir

function                                             old     new   delta
create_fs_device                                     125     158     +33
parse_word                                            41       -     -41
parse_escape                                          55       -     -55
fsck_main                                           2246    1893    -353
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 1/1 up/down: 33/-449)          Total: -416 bytes