fix squad eval
@yzhang123 it's this needed for tlt? if so, it should go to b4  > @yzhang123 it's this needed for tlt? if so, it should go to b4

I'm not sure about that status. @vladgets  could you take comment?
Fix error from Dec 17, 2020 https://github.com/NVIDIA/NeMo/pull/1569/files

Signed-off-by: Yang Zhang <yangzhang@nvidia.com>