ext4: bail early when clearing inode journal flag fails

When clearing inode journal flag, we call jbd2_journal_flush() to force
all the journalled data to their final locations. Currently we ignore
when this fails and continue clearing inode journal flag. This isn't a
big problem because when jbd2_journal_flush() fails, journal is likely
aborted anyway. But it can still lead to somewhat confusing results so
rather bail out early.

Coverity-id: 989044
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>