[media] siano: Use the default firmware for Stellar

The Stellar firmware load routine is different. Improve it to use
the default firmware, if no modprobe parameter tells otherwise.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Tested-by: André Roth <neolynx@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>