greybus: camera: Fix backword compatibility in configure streams

Configure streams ret code should be number of streams in
gb operation exported to HOST camera.
Until gb operation is migrated to new interface return
number of streams in ret code.

Signed-off-by: Gjorgji Rosikopulos <grosikopulos@mm-sol.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>