dm: core: Pass a root node to of_find_node_by_phandle()

This function currently assumes that the control FDT is used. Update it
to allow a root node to be passed, so it can work with any tree.

Also add a comment to ofnode_get_by_phandle() so that its purpose is
clear.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/of_access.c b/drivers/core/of_access.c
index df007e6..f7743d4 100644
--- a/drivers/core/of_access.c
+++ b/drivers/core/of_access.c
@@ -445,14 +445,15 @@
 	return np;
 }
 
-struct device_node *of_find_node_by_phandle(phandle handle)
+struct device_node *of_find_node_by_phandle(struct device_node *root,
+					    phandle handle)
 {
 	struct device_node *np;
 
 	if (!handle)
 		return NULL;
 
-	for_each_of_allnodes(np)
+	for_each_of_allnodes_from(root, np)
 		if (np->phandle == handle)
 			break;
 	(void)of_node_get(np);
@@ -697,7 +698,7 @@
 			 * below.
 			 */
 			if (cells_name || cur_index == index) {
-				node = of_find_node_by_phandle(phandle);
+				node = of_find_node_by_phandle(NULL, phandle);
 				if (!node) {
 					debug("%s: could not find phandle\n",
 					      np->full_name);
diff --git a/drivers/core/ofnode.c b/drivers/core/ofnode.c
index 42f3c09..b241be3 100644
--- a/drivers/core/ofnode.c
+++ b/drivers/core/ofnode.c
@@ -391,7 +391,7 @@
 	ofnode node;
 
 	if (of_live_active())
-		node = np_to_ofnode(of_find_node_by_phandle(phandle));
+		node = np_to_ofnode(of_find_node_by_phandle(NULL, phandle));
 	else
 		node.of_offset = fdt_node_offset_by_phandle(gd->fdt_blob,
 							    phandle);