kobject: documentation: Fix erroneous function example in kobject doc.

Update the definitions of some functions listed in the kobject
document, since they have been changed.

Signed-off-by: Qi Zheng <arch0.zheng@gmail.com>
Link: https://lore.kernel.org/r/20200505061828.42952-1-arch0.zheng@gmail.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>