ocfs2/quota: Release lock for error in ocfs2_quota_write.

ocfs2_quota_write needs to release the lock if it fails to
read quota block. So use "goto out" instead of "return err".

Signed-off-by: Tao Ma <tao.ma@oracle.com>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Joel Becker <joel.becker@oracle.com>