getCameraID: return -1 on error instead of 0

0 is a valid camera ID, so don't reuse that as error value.

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
mavconn-camera-opencv: set config in non-stereo modes as well

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
PxOpenCVCamera.cc: implement framerate setting

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>