nvme-pci: allocate tagset on reset if necessary

If a drive is unable to create IO queues on the initial probe, a
subsequent reset will need to allocate the tagset if IO queue creation
is successful. Without this, blk_mq_update_nr_hw_queues will crash on a
bad pointer due to the invalid tagset.

Fixes: eac3ef26 ("nvme-pci: split the initial probe from the rest path")
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>