media: i2c: adv748: Fix kerneldoc

The field is gone, remove the documentation.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>