rust: rbtree: add __rust_helper to helpers

This is needed to inline these helpers into Rust code.

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260105-define-rust-helper-v2-15-51da5f454a67@google.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: Darksonn

rust/helpers/rbtree.c

@@ -2,18 +2,19 @@
 
 #include <linux/rbtree.h>
 
-void rust_helper_rb_link_node(struct rb_node *node, struct rb_node *parent,
-			      struct rb_node **rb_link)
+__rust_helper void rust_helper_rb_link_node(struct rb_node *node,
+					    struct rb_node *parent,
+					    struct rb_node **rb_link)
 {
 	rb_link_node(node, parent, rb_link);
 }
 
-struct rb_node *rust_helper_rb_first(const struct rb_root *root)
+__rust_helper struct rb_node *rust_helper_rb_first(const struct rb_root *root)
 {
 	return rb_first(root);
 }
 
-struct rb_node *rust_helper_rb_last(const struct rb_root *root)
+__rust_helper struct rb_node *rust_helper_rb_last(const struct rb_root *root)
 {
 	return rb_last(root);
 }