nvmed: wrap namespaces in Some() so select() match arms unify (fix E0308)

The block feeding `let namespaces = match ... { Some(ns) => ns, None => exit }`
must yield Option, but the Either::Left arm returned the BTreeMap directly while
Either::Right returned None. Wrap Left in Some(namespaces).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

drivers/storage/nvmed/src/main.rs

@@ -101,7 +101,7 @@ fn daemon(daemon: daemon::Daemon, mut pcid_handle: PciFunctionHandle) -> ! {
         futures::pin_mut!(namespaces_future);
         futures::pin_mut!(time_future);
         match futures::future::select(namespaces_future, time_future).await {
-            futures::future::Either::Left((namespaces, _)) => namespaces,
+            futures::future::Either::Left((namespaces, _)) => Some(namespaces),
             futures::future::Either::Right(_) => None,
         }
     }) {