dvenc: fix 2x4x8 (interlaced) weight table

Since the decoder has been fixed to output something similar to
other implementations, the encoder weight table needed this fix.

Reference PSNR values on a progressive sequence (from tiny_psnr)
from a chained encoding and decoding:
Full progressive: stddev:    0.74 PSNR: 50.69 MAXDIFF:   19
Before:           stddev:    1.43 PSNR: 44.97 MAXDIFF:   17
This patch:       stddev:    0.76 PSNR: 50.44 MAXDIFF:   14

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>