rust: Fix x86 build

Signed-off-by: Hector Martin <marcan@marcan.st>

Author: marcan

rust/helpers.c

@@ -424,11 +424,13 @@ const struct of_device_id *rust_helper_of_match_device(
 }
 EXPORT_SYMBOL_GPL(rust_helper_of_match_device);
 
+#ifdef CONFIG_OF
 bool rust_helper_of_node_is_root(const struct device_node *np)
 {
 	return of_node_is_root(np);
 }
 EXPORT_SYMBOL_GPL(rust_helper_of_node_is_root);
+#endif
 
 struct device_node *rust_helper_of_parse_phandle(const struct device_node *np,
 		const char *phandle_name,

rust/kernel/of.rs

@@ -162,6 +162,11 @@ impl Node {
 
     /// Returns `true` if the node is the root node.
     pub fn is_root(&self) -> bool {
+        #[cfg(not(CONFIG_OF))]
+        {
+            false
+        }
+        #[cfg(CONFIG_OF)]
         unsafe { bindings::of_node_is_root(self.raw_node) }
     }