Reverting CfL bug introduced in code review.

The original code for od_resample_luma_coeffs correctly copied the
 down-sampled luma when chroma when bsize>0, but was derailed by an
 errant code review.
See comment: https://review.xiph.org/32/diff/35/src/intra.c#newcode463
Reverting this change gives a ~6% decrease in rate and ~0.3 dB
 improvement in PSNR for subset1, plane 1 (Cb); see below:

Normal block switching:

            RATE    DSNR
    PSNR -5.9405 0.26537
 PSNRHVS -5.7661 0.34183
    SSIM -6.4649 0.24499
FASTSSIM -7.5493 0.18921

Only 4x4 blocks:

            RATE    DSNR
    PSNR  1.6701 -0.080416
 PSNRHVS -1.7662  0.11160
    SSIM  1.7615 -0.061370
FASTSSIM -0.96156 0.024629

Only 8x8 blocks:

            RATE    DSNR
    PSNR -8.2539 0.40603
 PSNRHVS -5.8062 0.37810
    SSIM -9.5547 0.38005
FASTSSIM -9.0039 0.26007

Only 16x16 blocks:

            RATE    DSNR
    PSNR -4.1532 0.16922
 PSNRHVS -5.8759 0.31451
    SSIM -3.3665 0.12975
FASTSSIM -7.5254 0.15857