update softmax evaluate for dynamic shape input (#4638)
update softmax evaluate for dynamic shape input (#4638)

Co-authored-by: Scott Cyphers <7bb9a997e5f2906b81b1e1515637af43501e2590@users.noreply.github.com>
NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph