[media] tw2804: Revert ADC Control commit 523a4f7f

Case: In AdLink MPG24 there is bt878 exists (it captures one frame of all video
inputs), Video Signal for it one transmits through tw2804 chip, so we can't
control ADC (shut on/off) on tw2804, as some another can use bttv capture way.

Signed-off-by: Volokh Konstantin <volokh84@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>