[media] radio-si470x: Lower firmware version requirements

Testing with a firmware version 12 usb radio stick has shown version 12
to work fine too.

Reported-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>