Reduced bias in picking loop filter level

Reduced bias in picking loop filter level

The bias in picklpf intended to bias toward less greedy in getting
best frame level psnr while maximize overall quality for a clip.
This commit reduced the bias for frames using 8x8 transform to
achieve better compression overall.

The change improve compression by ~.15% consistently on most of the
HD clips tested.

http://www.corp.google.com/~yaowu/no_crawl/LPFBias_FixSkip.html

Change-Id: Ic30932d2b8eaebd52339b0195f569edc48eed7bc