V4L/DVB (6821): s5h1409: fix IF frequency configuration

On the s5h1409 demod, the IF frequency for VSB is limited to 44 / 5.38 MHz.

Hardcode VSB IF frequency within the driver to 44 / 5.38 MHz.
QAM IF frequency remains configurable via attach-time configuration.

Acked-by: Steven Toth <stoth@hauppauge.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>