[media] DocBook: Fix false positive undefined ioctl references

The new code that detects undocumented ioctls hits some false
positives:

This one is not documented, nor it should, as this is
there just to reserve namespace:

	Warning: can't find reference for VIDIOC_RESERVED ioctl

But those are already documented together with other ioctls:

	Warning: can't find reference for VIDIOC_UNSUBSCRIBE_EVENT ioctl
	Warning: can't find reference for FE_GET_PROPERTY ioctl
	Warning: can't find reference for VIDIOC_SUBDEV_G_EDID ioctl
	Warning: can't find reference for VIDIOC_SUBDEV_S_EDID ioctl
	Warning: can't find reference for VIDIOC_SUBDEV_S_DV_TIMINGS ioctl
	Warning: can't find reference for VIDIOC_SUBDEV_G_DV_TIMINGS ioctl
	Warning: can't find reference for VIDIOC_SUBDEV_QUERY_DV_TIMINGS ioctl

So, we need to just be sure to point to the right documentation.

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