avcodec/snowenc: simplify spatial_decomposition_count seting code

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/snowdec: return more specific error codes

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/snowdec: forward error codes

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/snowdec: also print qbias and mvscale in debug output

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