[media] ds3000: fix LNB supply voltage on Tevii S480 on initialization

The Tevii S480 outputs 18V on startup for the LNB supply voltage and does not
automatically power down. This blocks other receivers connected
to a satellite channel router (EN50494), since the receivers can not send the
required DiSEqC sequences when the Tevii card is connected to a the same SCR.

This patch switches off the LNB supply voltage on initialization of the frontend.

[mchehab@osg.samsung.com: add a comment about why we're explicitly
 turning off voltage at device init]
Cc: stable@vger.kernel.org
Signed-off-by: Ulrich Eckhardt <uli@uli-eckhardt.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>