fix regression where we failed to pick up optimized paths due to constness difference
fix regression where we failed to pick up optimized paths due to constness difference

efeguney/gemmlowp,google/gemmlowp,maciekcc/gemmlowp,petewarden/gemmlowp,miaowang14/gemmlowp,google/gemmlowp,petewarden/gemmlowp,maciekcc/gemmlowp,efeguney/gemmlowp,efeguney/gemmlowp,google/gemmlowp,google/gemmlowp,petewarden/gemmlowp,miaowang14/gemmlowp,dave-andersen/gemmlowp,dave-andersen/gemmlowp,petewarden/gemmlowp,maciekcc/gemmlowp,miaowang14/gemmlowp,dave-andersen/gemmlowp