common: minor fixes in digital filter
common: minor fixes in digital filter

ApolloAuto/apollo,jinghaomiao/apollo,ApolloAuto/apollo,jinghaomiao/apollo,jinghaomiao/apollo,jinghaomiao/apollo,xiaoxq/apollo,ycool/apollo,xiaoxq/apollo,ycool/apollo,ycool/apollo,ApolloAuto/apollo,ycool/apollo,xiaoxq/apollo,ApolloAuto/apollo,ycool/apollo,jinghaomiao/apollo,ApolloAuto/apollo,xiaoxq/apollo,ApolloAuto/apollo,xiaoxq/apollo,jinghaomiao/apollo,ycool/apollo,xiaoxq/apollo