When setting the EDID it would attempt to update two controls
that are only present if there is an HDMI output configured.

If there isn't any (e.g. when the vivid module is loaded with
node_types=1), then calling VIDIOC_S_EDID would crash.

Fix this by first checking if outputs are present.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>