f2fs: do not recover wrong data index

During the roll-forward recovery, if we found a new data index written fsync
lastly, we need to recover new block address.
But, if that address was corrupted, we should not recover that.
Otherwise, f2fs gets kernel panic from:

 In check_index_in_prev_nodes(),

    sentry = get_seg_entry(sbi, segno);
             --------------------------> out-of-range segno.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>