iommu_gas: reduce lower bound checking in lowermatch

[dougm]

Summary

The loop iteration in iommu_gas_lowermatch checks the bound a->common->lowaddr twice per loop iteration. Rewrite to test only once per iteration.

[alc]

sys/dev/iommu/iommu_gas.c

432–433

I don't think that there is any advantage to having this early return. In other words, the next if statement might as well begin with entry != NULL &&.

436

I'm not sure that there is a point to this test.

[dougm]

Do not worry about passing to iommu_gas_match_one a range wholly beyond lowaddr. Since that function checks the upper end of the range against lowaddr, it'll get rejected there.