staging: bcm2835-audio: update TODO

staging: bcm2835-audio: update TODO

The following tasks were completed or not the right solution:

1/2- Not the proper solution, we should register a platform device in
vchiq the same way it's done with bcm2835-camera as commented here:
https://lkml.org/lkml/2018/10/16/1131

2/3- Fixed by Takashi Iwai here: https://lkml.org/lkml/2018/9/4/587

Also, adds a new task as per mailing list conversation.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>