Documentation: update debugobjects doc

Documentation: update debugobjects doc

Update documentation creangponding to change(debugobjects: make fixup
functions return bool instead of int).

Signed-off-by: Du, Changbin <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Josh Triplett <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>