V4L/DVB (10314): cx25840: ignore TUNER_SET_CONFIG in the command callback.

These days TUNER_SET_CONFIG is broadcast to the other i2c devices
and that triggers a fw load on the cx25840. Ignore this command
since cx25840 isn't a tuner and you really do not want to load
the firmware that early.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>