vmm: Fix clippy: for_kv_map

Fix use of a paired map iterator when only the values are cared about.

Signed-off-by: Rob Bradford <rbradford@meta.com>

vmm/src/device_tree.rs

@@ -114,7 +114,7 @@ impl<'a> BftIter<'a> {
         let mut nodes = Vec::with_capacity(hash_map.len());
         let mut i = 0;
 
-        for (_, node) in hash_map.iter() {
+        for node in hash_map.values() {
             if node.parent.is_none() {
                 nodes.push(node);
             }