media: cx231xx: Ignore an i2c mux adapter

Hauppauge 935C cannot communicate with the si2157
when using the mux adapter returned by the si2168,
so disable it to fix the device.

Signed-off-by: Brad Love <brad@nextdimension.cc>
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>