dvbdevice: Fix DiSEqC LNBf satellite select

Due to a bug at libdvbv5, it was not possible to select satellite 0.

That induced a bug at Kaffeine of assuming that satNumber = 0 would
mean to disable DiSEqC, with is wrong.

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