staging: tidspbridge: Remove cfg_set_object()

As the services directory is going to be removed, the cfg_set_object
function has also to be removed.

Since the driver object handle is retrieved from the drv_data structure,
then the word "Registry" is replaced by "driver data" in the comments.

Signed-off-by: Ivan Gomez Castellanos <ivan.gomez@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>