rust: xarray: 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>
Acked-by: Tamir Duberstein <tamird@gmail.com>
Link: https://lore.kernel.org/r/20260105-define-rust-helper-v2-27-51da5f454a67@google.com
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

Author: Darksonn

rust/helpers/xarray.c

@@ -2,27 +2,27 @@
 
 #include <linux/xarray.h>
 
-int rust_helper_xa_err(void *entry)
+__rust_helper int rust_helper_xa_err(void *entry)
 {
 	return xa_err(entry);
 }
 
-void rust_helper_xa_init_flags(struct xarray *xa, gfp_t flags)
+__rust_helper void rust_helper_xa_init_flags(struct xarray *xa, gfp_t flags)
 {
 	return xa_init_flags(xa, flags);
 }
 
-int rust_helper_xa_trylock(struct xarray *xa)
+__rust_helper int rust_helper_xa_trylock(struct xarray *xa)
 {
 	return xa_trylock(xa);
 }
 
-void rust_helper_xa_lock(struct xarray *xa)
+__rust_helper void rust_helper_xa_lock(struct xarray *xa)
 {
 	return xa_lock(xa);
 }
 
-void rust_helper_xa_unlock(struct xarray *xa)
+__rust_helper void rust_helper_xa_unlock(struct xarray *xa)
 {
 	return xa_unlock(xa);
 }