make call to get IR object more direct

[vtjnash]

Avoids the world age problem with code_lowered

[vtjnash]

@IanButterworth

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (62d5f42) 74.98% compared to head (42c3e43) 74.98%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #112 +/- ## ======================================= Coverage 74.98% 74.98% ======================================= Files 15 15 Lines 1419 1419 ======================================= Hits 1064 1064 Misses 355 355 ``` | [Impacted Files](https://codecov.io/gh/FluxML/IRTools.jl/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Flux) | Coverage Δ | | |---|---|---| | [src/eval.jl](https://codecov.io/gh/FluxML/IRTools.jl/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Flux#diff-c3JjL2V2YWwuamw=) | `94.11% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Flux). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Flux)

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[IanButterworth]

Fixes #111

[maleadt]

This is included in https://github.com/FluxML/IRTools.jl/pull/109.