media: cedrus: Cleanup control initialization

In order to introduce other controls, the control initialization
needs to support an initial struct v4l2_ctrl_control.

While here, let's cleanup the control initialization,
removing unneeded fields.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>