kill f_dentry uses

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 1d51968..27b0c91 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -367,8 +367,8 @@
  * struct cftype: handler definitions for cgroup control files
  *
  * When reading/writing to a file:
- *	- the cgroup to use is file->f_dentry->d_parent->d_fsdata
- *	- the 'cftype' of the file is file->f_dentry->d_fsdata
+ *	- the cgroup to use is file->f_path.dentry->d_parent->d_fsdata
+ *	- the 'cftype' of the file is file->f_path.dentry->d_fsdata
  */
 
 /* cftype->flags */