XGLM - Fix Softmax NaNs when using FP16 (#18057)
* fix fp16 for xglm
* Removed misleading comment
* Fix undefined variable
Co-authored-by: Gabriele Sarti <gsarti@amazon.com>
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>
