NVMe: Delete only created queues

Use the online queue count instead of the number of allocated queues. The
controller should just return an invalid queue identifier error to the
commands if a queue wasn't created. While it's not harmful, it's still
not correct.

Reported-by: Saar Gross <saar@annapurnalabs.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>