[PATCH] nvme-pci: avoid dereference of symbol from unloaded module

[Sagi Grimberg]

>> The nvme_wq is shared by all kinds of host(PCI, FC, ...), so
>> not good to flush all queued work in 'nvme_wq' just before
>> removing pci host module only.
>>
>> Not mention 'remove_work' is actually scheduled by system wq
>> instead of nvme_wq.
> 
> Still seems better than messing with module reference counts.

And also does not change the behavior (failing module unload).