[media] drivers/media/usb/as102: constify as102_priv_ops_t structure

The as102_priv_ops_t structure is never modified, so declare it as
const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>