nvme-pci: flush initial scan_work for async probe

The nvme device may have a namespace with the root partition, so make
sure we've completed scanning before returning from the async probe.

Fixes: eac3ef262941 ("nvme-pci: split the initial probe from the rest path")
Reported-by: Klaus Jensen <its@irrelevant.dk>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 1ff8843..c734934c 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -3102,6 +3102,7 @@
 
 	nvme_start_ctrl(&dev->ctrl);
 	nvme_put_ctrl(&dev->ctrl);
+	flush_work(&dev->ctrl.scan_work);
 	return 0;
 
 out_disable: