nvme-pci: do not set the NUMA node of device if it has none

If a device has no NUMA node information associated with it, the driver
puts the device in node first_memory_node (say node 0). Not having a
NUMA node and being associated with node 0 are completely different
things and it makes little sense to mix the two.

Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>