rust: pwm: Update ARef and AlwaysRefCounted imports to use sync::aref

Update call sites in `pwm.rs` to import `ARef` and `AlwaysRefCounted`
from `sync::aref` instead of `types`.

This aligns with the ongoing effort to move `ARef` and
`AlwaysRefCounted` to sync.

Suggested-by: Benno Lossin <lossin@kernel.org>
Link: #1173
Signed-off-by: Shankari Anand <shankari.ak0208@gmail.com>
Acked-by: Michal Wilczynski <m.wilczynski@samsung.com>
Link: https://patch.msgid.link/20251123092438.182251-7-shankari.ak0208@gmail.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Author: Shankari02

rust/kernel/pwm.rs

@@ -13,7 +13,8 @@ use crate::{
     devres,
     error::{self, to_result},
     prelude::*,
-    types::{ARef, AlwaysRefCounted, Opaque}, //
+    sync::aref::{ARef, AlwaysRefCounted},
+    types::Opaque, //
 };
 use core::{marker::PhantomData, ptr::NonNull};