[media] cx25840: fix cx25840_s_stream for cx2388x and cx231xx

For those two devices the code wrote to addresses 0x115/6, but on
those devices those addresses have nothing to do with power controls.
So clearly this never worked. Rather than writing to bogus addresses,
just do nothing for the cx2388x and cx231xx.

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