media: sun6i-csi: Remove controls handler from the driver

The driver does not expose controls directly and thus does not need
a controls handler for its own use.

Controls attached to subdevs used to be exposed that way, however this
can easily lead to issue when multiple subdevs attached to the same
v4l2 device expose the same controls. Subdev controls should be set
through each individual subdev node instead.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>