bhyve: unsigned <= 0

[tsoome]

Summary

illumos smatch build is complaining:

pci_nvme_parse_config() warn: 'sc->max_qentries' unsigned <= 0
pci_nvme_parse_config() warn: 'sc->ioslots' unsigned <= 0

Because we are using atoi() to translate string to int, we need
to use int type variable for translation.