fixed the scaling in 8x8 trellis quant

This commit has a few minor fixes to the 8x8 trellis quant, so to
make it work regardless if extend_qrange is enabled or not. It also
borrowed adaptive RDMULT constants from 4x4 trellis that was missed
in the 8x8 trellis quant.

Change-Id: I60d7769071f102c699b5084597e62bca87a1f759