[media] DocBook media: fix xv601/709 formulas
[media] DocBook media: fix xv601/709 formulas

The denominator for the scaling and offsets is 256, not 255. Fix this.

Signed-off-by: Hans Verkuil <3a513708f73c27e7d36ebc496aa41dad6a3153ea@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <ad86ba2154032c9f55743a190faa2459a9d61d42@osg.samsung.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs