Fix vector widths of constants in fast_log and fast_exp
Fix vector widths of constants in fast_log and fast_exp

dougkwan/Halide,tdenniston/Halide,ronen/Halide,dougkwan/Halide,kgnk/Halide,jiawen/Halide,adasworks/Halide,ronen/Halide,ronen/Halide,adasworks/Halide,jiawen/Halide,tdenniston/Halide,tdenniston/Halide,dougkwan/Halide,jiawen/Halide,kgnk/Halide,dougkwan/Halide,kgnk/Halide,tdenniston/Halide,psuriana/Halide,tdenniston/Halide,kgnk/Halide,adasworks/Halide,adasworks/Halide,adasworks/Halide,kgnk/Halide,ronen/Halide,jiawen/Halide,psuriana/Halide,jiawen/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,jiawen/Halide,adasworks/Halide,jiawen/Halide,tdenniston/Halide,kgnk/Halide,ronen/Halide,tdenniston/Halide,ronen/Halide,dougkwan/Halide,adasworks/Halide,ronen/Halide,dougkwan/Halide,kgnk/Halide,psuriana/Halide,dougkwan/Halide,dougkwan/Halide,ronen/Halide,psuriana/Halide,psuriana/Halide,tdenniston/Halide,adasworks/Halide