[media] si2168: few firmware download changes

Rework firmware selection logic a little bit.
Print notice asking user update firmware when old Si2168 B40
firmware is used.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Tested-by: Olli Salonen <olli.salonen@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>