[media] v4l: omap4iss: Don't initialize fields to 0 manually

The iss_device structure is allocated with kzalloc, there's no need to
initialize its fields to 0 explicitly.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>