Revert "driver core: move knode_driver into private structure"

This reverts commit 93e746db.

Turns out that device_initialize shouldn't fail silently.
This series needs to be reworked in order to get into proper
shape.

Reported-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>