We should update age extent in f2fs_do_zero_range() like we
did in f2fs_truncate_data_blocks_range().

Fixes: 71644dff ("f2fs: add block_age-based extent cache")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>