[PATCH] nvme: don't call blk_mq_{,un}quiesce_tagset when ctrl->tagset is NULL

[Sagi Grimberg]

>> All the other drivers check that they have IO queues before
>> quiescing/unquiescing them.
> 
> The core firmware activation code does not.

Well, ideally it should, but maybe it would be more readable
if we condition on ctrl->queue_count > 1.