nvme: Give up when we've failed

[imp]

Summary

Normally, we poll the device every so often to see if commands have
timed out. However, we'll go into the recovery state as part of failing
the drive. To account for all possibilties, if we're failed when we get
into the polling function, just stop polling: Party is over.

Sponsored by: Netflix

[imp]

It turns out there's a better way to do this: If we create a new state for failed qpairs, then we can do some other checks.
https://reviews.freebsd.org/D41866 has that idea fully explored. Once that's ready to go, I plan on abandoning this.