bhyve: check upper bounds for value from qsz

[tsoome]

Summary

The max_qentries in pci_nvme_softc is uint16_t and
too large int may get truncated to invalid value.
While there, use local declarations for val.

Suggested by: Bill Sommerfeld

[bnovkov]

usr.sbin/bhyve/pci_nvme.c

3188

Why aren't we defining val at the start of the function anymore?

[chuck]

Assuming you restore the declaration of val as @bnovkov suggested, LGTM.

[tsoome]

declare val at the beginning of function.