[media] tda10071: force modulation to QPSK on DVB-S

Only supported modulation for DVB-S is QPSK. Modulation parameter
contains invalid value for DVB-S on some cases, which leads driver
refusing tuning attempt. Due to that, hard code modulation to QPSK
in case of DVB-S.

Cc: stable@vger.kernel.org
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>