sysfs.txt: fix pre-kernfs sysfs_dirent reference

sysfs_dirent went away when kernfs was extracted from sysfs. The reference
to the kobject now lives in a kernfs_node (in the 'priv' member).

See commit 324a56e16e ("kernfs: s/sysfs_dirent/kernfs_node/ and rename
its friends accordingly").

Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/sysfs.txt

@@ -40,7 +40,7 @@ ancestors of object hierarchies; i.e. the subsystems the objects
 belong to. 
 
 Sysfs internally stores a pointer to the kobject that implements a
-directory in the sysfs_dirent object associated with the directory. In
+directory in the kernfs_node object associated with the directory. In
 the past this kobject pointer has been used by sysfs to do reference
 counting directly on the kobject whenever the file is opened or closed.
 With the current sysfs implementation the kobject reference count is