[media] si2168: return error if set_frontend is called with invalid parameters

This patch should is based on Antti's silabs branch.

According to dvb-frontend.h set_frontend may be called with bandwidth_hz set to 0 if automatic bandwidth is required. Si2168 does not support automatic bandwidth and does not declare FE_CAN_BANDWIDTH_AUTO in caps.

This patch will change the behaviour in a way that EINVAL is returned if bandwidth_hz is 0.

Signed-off-by: Olli Salonen <olli.salonen@iki.fi>
Reviewed-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>