f2fs: fix to update age extent correctly during truncation

nr_free may be less than len, we should update age extent cache
w/ range [fofs, len] rather than [fofs, nr_free].

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>

fs/f2fs/file.c

@@ -617,7 +617,7 @@ void f2fs_truncate_data_blocks_range(struct dnode_of_data *dn, int count)
 		fofs = f2fs_start_bidx_of_node(ofs_of_node(dn->node_page),
 							dn->inode) + ofs;
 		f2fs_update_read_extent_cache_range(dn, fofs, 0, len);
-		f2fs_update_age_extent_cache_range(dn, fofs, nr_free);
+		f2fs_update_age_extent_cache_range(dn, fofs, len);
 		dec_valid_block_count(sbi, dn->inode, nr_free);
 	}
 	dn->ofs_in_node = ofs;