[media] adv7604: Correct G/S_EDID behaviour

In order to have v4l2-compliance tool pass the G/S_EDID some modifications
where needed in the driver.
In particular, the edid.reserved zone must be blanked.

Based on a patch from Jean-Michel Hautbois <jean-michel.hautbois@vodalys.com>,
but reworked it a bit. It should use 'data' (which depends on edid.present)
instead of edid.blocks as the check whether edid data is present.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>