nvme-pci: ensure we're polling a polled queue

In the Linux kernel, the following vulnerability has been resolved:

nvme-pci: ensure we're polling a polled queue

A user can change the polled queue count at run time. There's a brief

window during a reset where a hipri task may try to poll that queue

before the block layer has updated the queue maps, which would race with

the now interrupt driven queue and may cause double completions.