doc-rst: linux_tv: use Example x.y. instead of a single number

doc-rst: linux_tv: use Example x.y. instead of a single number

On the example captions, use always <chapter>.<number>., because:
1) it matches the DocBook;
2) it would mean less changes if we need to add a new example,
as only one chapter will be affected.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>