[media] media: Use correct ioctl name in MEDIA_IOC_SETUP_LINK documentation

The documentation incorrectly refers to MEDIA_IOC_ENUM_LINKS, fix it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>