media: em28xx: driver supports two frontends, but not i2c clients

media: em28xx: driver supports two frontends, but not i2c clients

Fix em28xx driver to accommodate a device with two i2c client demods.

The em28xx driver already had a multi frontend aware device struct,
with two fe, just not two i2c client demods. Since Hauppauge HVR975
has transitioned from cx231xx to em2828X, this is required for full
functionality of the devices.

Signed-off-by: Bradford Love <brad@nextdimension.cc>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>