e2fsck: exit with exit status 0 if no errors were fixed

e2fsck: exit with exit status 0 if no errors were fixed

Previously, e2fsck would exit with a status code of 1 even though the
only changes that it made to the file system were various
optimziations and not fixing file system corruption.  Since the man
page states that an exit status of 1 means "file system errors
corrupted", fix e2fsck to return an exit status of 0.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>