Currently the -D option is essentially defunct since it's the root,
where we are going to corrupt a dir item is always set to the tree
root. Fix this by passing the root from the "-r" option. Aditionally
convert the interface for this option to the new format. So if one
wants to corrupt a dir item in the default fs tree, they should now
invoke:

 btrfs-corrupt-block -r 5 -D <objectid,DIR_ITEM,offset> -f name

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>