Improved aom_smooth_predictor_16x 32,16,8
Improved aom_smooth_predictor_16x 32,16,8

Tests showed the following improvements:
16x32: ~9.2%
16x16: ~6.9%
16x8: ~3.2%

Change-Id: Id9f23928cde28ba450ba941415f9fcdf04d620c3

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom