Return error from si2168_cmd_execute in case the demodulator returns an
error.
Signed-off-by: NOlli Salonen <olli.salonen@iki.fi>
Signed-off-by: NAntti Palosaari <crope@iki.fi>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>