fsck: fix incorrect handling of child exit

fsck: fix incorrect handling of child exit

In commit

  c4fb8c6a - fsck: do not use statics

not only statics were changed but also a couple of
statics-unrelated changes were made.

This included the handling of the child termination status
as follows:

    - if (WIFEXITED(status))
    -   status = WEXITSTATUS(status);
    - else if (WIFSIGNALED(status)) {
    + status = WEXITSTATUS(status);
    + if (WIFSIGNALED(status)) {

This is wrong, should have used a different variable to hold exit code.

Reported by Niklas Hambüchen <mail@nh2.me>.

function                                             old     new   delta
wait_one                                             294     282     -12

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