nvme_metrics: use device label in namespace_info metric

Use "device" rather than "namespace" label so that it matches the other
namespace-specific metrics.

Signed-off-by: Daniel Swarbrick <daniel.swarbrick@gmail.com>

nvme_metrics.py

@@ -117,7 +117,7 @@
     "namespace_info": Info(
         "namespace",
         "Namespace information",
-        ["namepace", "nsid", "controller"], namespace=namespace, registry=registry,
+        ["device", "nsid", "controller"], namespace=namespace, registry=registry,
     ),
     "physical_size": Gauge(
         "physical_size_bytes",