firesat: fix DVB-S2 device recognition

This only makes sure that a DVB-S2 device is really recognized as a S2,
nothing else is added yet. It's using the string containing the model
that is stored in the configuration ROM, the older version was using
some hardware revision dependent part of the ROM.

Signed-off-by: Ben Backx <ben@bbackx.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>