fsck: more clever (->smaller) handling of parameters

fsck: more clever (->smaller) handling of parameters

function                                             old     new   delta
fsck_device                                          213     449    +236
new_args                                               -      46     +46
fsck_main                                           1870    1815     -55
execute                                              289       -    -289
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(add/remove: 1/1 grow/shrink: 1/1 up/down: 282/-344)          Total: -62 bytes

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