This change does not impact the bitstream as no loss is incured by using
a fixed point value for the transform size average.

For low bit depth, the transform size average is stored using Q8.10
fixed point format. Worst case, smallest fraction is 1/1024.

Results on Subset1 (Compared to 366b74 with CfL)

  PSNR | PSNR Cb | PSNR Cr | PSNR HVS |   SSIM | MS SSIM | CIEDE 2000
0.0000 |  0.0000 |  0.0000 |   0.0000 | 0.0000 |  0.0000 |     0.0000

Change-Id: Ia5b046b92a0e4c40e413b16af3394bdc0a8c8cd9