fix data type of coeff_t
fix data type of coeff_t

guanzidashu/guetzli_ios_metal,guanzidashu/guetzli_ios_metal,ianhuang-777/guetzli,ianhuang-777/guetzli,guanzidashu/guetzli_ios_metal,ianhuang-777/guetzli,guanzidashu/guetzli_ios_metal,ianhuang-777/guetzli