nvme-pci: only set nr_maps to 2 if poll queues are supported

The block layer now enables polling support on a queue if nr_maps
includes the poll map, so we should only set that if we actually
support poll queues.

Fixes:  6544d229bf ("block: enable polling by default if a poll map is initalized")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

drivers/nvme/host/pci.c

@@ -2289,6 +2289,9 @@ static int nvme_dev_add(struct nvme_dev *dev)
 	if (!dev->ctrl.tagset) {
 		dev->tagset.ops = &nvme_mq_ops;
 		dev->tagset.nr_hw_queues = dev->online_queues - 1;
+		dev->tagset.nr_maps = 2; /* default + read */
+		if (dev->io_queues[HCTX_TYPE_POLL])
+			dev->tagset.nr_maps++;
 		dev->tagset.nr_maps = HCTX_MAX_TYPES;
 		dev->tagset.timeout = NVME_IO_TIMEOUT;
 		dev->tagset.numa_node = dev_to_node(dev->dev);