rust: refcount: 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>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://patch.msgid.link/20260105-define-rust-helper-v2-17-51da5f454a67@google.com

Author: Darksonn

rust/helpers/refcount.c

@@ -2,27 +2,27 @@
 
 #include <linux/refcount.h>
 
-refcount_t rust_helper_REFCOUNT_INIT(int n)
+__rust_helper refcount_t rust_helper_REFCOUNT_INIT(int n)
 {
 	return (refcount_t)REFCOUNT_INIT(n);
 }
 
-void rust_helper_refcount_set(refcount_t *r, int n)
+__rust_helper void rust_helper_refcount_set(refcount_t *r, int n)
 {
 	refcount_set(r, n);
 }
 
-void rust_helper_refcount_inc(refcount_t *r)
+__rust_helper void rust_helper_refcount_inc(refcount_t *r)
 {
 	refcount_inc(r);
 }
 
-void rust_helper_refcount_dec(refcount_t *r)
+__rust_helper void rust_helper_refcount_dec(refcount_t *r)
 {
 	refcount_dec(r);
 }
 
-bool rust_helper_refcount_dec_and_test(refcount_t *r)
+__rust_helper bool rust_helper_refcount_dec_and_test(refcount_t *r)
 {
 	return refcount_dec_and_test(r);
 }