[media] i2c/adv7511: Fix license, set to GPL v2

Header claims GPL v2, so make the MODULE_LICENSE reflect that properly.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>