avcodec/lagarithrac.h/lag_get_rac: drop apparently unneeded operations
avcodec/lagarithrac: increase LUT from 256 to 1024 bytes

about 2 cycles (~1%) faster lag_get_rac()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/lagarithrac: lag_get_rac: use normal division

maybe 0.3% faster and simpler code