arvsystem: fix error in index comparison.
arvsystem: fix error in index comparison.

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