除以2

assign dc_avg = dc_avg1[12:2] + dc_avg2[12:3] + dc_avg3[12:3];

2592>>3+2592>>2+2592>>3 == 2592/2

  2592*（1>>3+1>>3+1>>2)
=2592*（1/8+1/8+1/4)
=2592*(1/2)

右移一位至關於除以2，左移一位至關於乘以2