udf: Do not update file length for failed writes to inline files

When write to inline file fails (or happens only partly), we still
updated length of inline data as if the whole write succeeded. Fix the
update of length of inline data to happen only if the write succeeds.

Reported-by:  <syzbot+0937935b993956ba28ab@syzkaller.appspotmail.com>
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>