arv_camera: fix the minimum value for the ROI offsets.
arv_camera: fix the minimum value for the ROI offsets.

The current code start ROI offsets from 1, but my camera (prosilica GC1020)
starts from 0.

lu-zero/aravis,AnilRamachandran/aravis,AnilRamachandran/aravis,lu-zero/aravis,AravisProject/aravis,AnilRamachandran/aravis,AravisProject/aravis,AravisProject/aravis,AnilRamachandran/aravis,lu-zero/aravis,AravisProject/aravis,AravisProject/aravis,AnilRamachandran/aravis,lu-zero/aravis,lu-zero/aravis