nvme-tcp: simplify nvme_tcp_teardown_io_queues()

As nvme_tcp_teardown_io_queues() is the only one caller of
nvme_tcp_destroy_admin_queue(), so we can merge it into
nvme_tcp_teardown_io_queues() to simplify the code.

Signed-off-by: Chunguang.xu <chunguang.xu@shopee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>