Only error out when the number of kernels being registered exceeds the limit (#1487)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1487

As titled. In some of the CI failures such as this one: https://github.com/pytorch/executorch/actions/runs/7331918023/job/19965267429?pr=1485#step:11:1520

The error message is confusing:
```
The total number of kernels to be registered is larger than the limit 17. 15 kernels are already registered and we're trying to register another 2 kernels.
```

Here I'm changing the ">=" condition to be ">" so that the error message makes sense.

Reviewed By: lucylq

Differential Revision: D52422427

fbshipit-source-id: 645d38bb1b52f27e525016984552a29f06e54ac0