media: staging: ipu3-imgu: No need for kernel-doc comments in driver struct

This part is rather trivial so adding more comments isn't really helpful.

Reported-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>