Function decode_mb_i16x16 

fn decode_mb_i16x16(
    r: &mut BitReader<'_>,
    st: &mut DecState,
    mb_x: u32,
    mb_y: u32,
    qp: &mut i32,
    mb_type: u32,
    pps: &Pps,
) -> Result<(), &'static str>