DVB: firedtv: FireDTV S2 problems with tuning solved

Signed-off-by: Beat Michel Liechti <bml303@gmail.com>
Tuning was broken on FireDTV S2 (and presumably  FloppyDTV S2) because a
wrong opcode was sent.  The box only gave "not implemented" responses.
Changing the opcode to _TUNE_QPSK2 fixes this for good.

Cc: stable@kernel.org
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>