Fix timm-efficientdet output (#998)
Summary:
We should output Tuple of tensors in the `eval()` function.
Pull Request resolved: https://github.com/pytorch/benchmark/pull/998
Reviewed By: erichan1
Differential Revision: D37523353
Pulled By: xuzhao9
fbshipit-source-id: 0f9a76c96a3d2e090ab651a51b06147ddec11ad1
