misc: fix broken libmagic interaction with plausibility check

If we get as far as calling libmagic, return the correct error code so
that mkfs asks for confirmation if libmagic finds something and
doesn't ask if nothing is found.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
4 files changed