V4L/DVB (7395): saa7134: start 2nd LND supply of Medion cards only if needed

The ISL6405 LNB supply is used on several Creatix / Medion cards. But only
the MD8800 needs its second section. So don't start it unless it is needed.

Signed-off-by: Hartmut Hackmann <hartmut.hackmann@t-online.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>