rust: poll: add __rust_helper to helpers

This is needed to inline these helpers into Rust code.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251202-define-rust-helper-v1-29-a2e13cbc17a6@google.com
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Darksonn

rust/helpers/poll.c

@@ -3,8 +3,9 @@
 #include <linux/export.h>
 #include <linux/poll.h>
 
-void rust_helper_poll_wait(struct file *filp, wait_queue_head_t *wait_address,
-			   poll_table *p)
+__rust_helper void rust_helper_poll_wait(struct file *filp,
+					 wait_queue_head_t *wait_address,
+					 poll_table *p)
 {
 	poll_wait(filp, wait_address, p);
 }