dm: core: Split ofnode_path_root() into two functions

This function turns out to be a little confusing since it looks up a path
and also registers the tree. Split it into two, one that gets the root
node and one that looks up a path, so the purpose is clear.

Registering the tree will happen in a function to be added in a later
patch, called oftree_from_fdt().

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/ofnode.h b/include/dm/ofnode.h
index a53cffb..ad179a6 100644
--- a/include/dm/ofnode.h
+++ b/include/dm/ofnode.h
@@ -855,18 +855,28 @@
 ofnode ofnode_path(const char *path);
 
 /**
- * ofnode_path_root() - find a node by full path from a root node
+ * oftree_path() - find a node by full path from a root node
  *
  * @tree: Device tree to use
  * @path: Full path to node, e.g. "/bus/spi@1"
  * Return: reference to the node found. Use ofnode_valid() to check if it exists
  */
-ofnode ofnode_path_root(oftree tree, const char *path);
+ofnode oftree_path(oftree tree, const char *path);
+
+/**
+ * oftree_root() - get the root node of a tree
+ *
+ * @tree: Device tree to use
+ * Return: reference to the root node
+ */
+ofnode oftree_root(oftree tree);
 
 /**
  * ofnode_read_chosen_prop() - get the value of a chosen property
  *
- * This looks for a property within the /chosen node and returns its value
+ * This looks for a property within the /chosen node and returns its value.
+ *
+ * This only works with the control FDT.
  *
  * @propname: Property name to look for
  * @sizep: Returns size of property, or  `FDT_ERR_...` error code if function