[media] smiapp: Use 8-bit reads only before identifying the sensor

Some sensors only allow 8-bit access, so use safe 8-bit access before the
sensor has been identified.

Signed-off-by: Sakari Ailus <sakari.ailus@maxwell.research.nokia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>