media: vivid: potential integer overflow in vidioc_g_edid()

If we pick a very large "edid->blocks" value then the "edid->start_block
+ edid->blocks" addition could wrap around.

Fixes: ef834f78 ("[media] vivid: add the video capture and output parts")

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>