rust: aref: use the "kernel vertical" imports style

Convert the imports to use the "kernel vertical" imports style [1].

No functional changes intended.

Link: https://docs.kernel.org/rust/coding-guidelines.html#imports [1]
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://patch.msgid.link/20260604-unique-ref-v17-8-7b4c3d2930b9@kernel.org
[ Picked from larger series and reworded. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/sync/aref.rs

@@ -17,7 +17,12 @@
 //! [`Arc`]: crate::sync::Arc
 //! [`Arc<T>`]: crate::sync::Arc
 
-use core::{marker::PhantomData, mem::ManuallyDrop, ops::Deref, ptr::NonNull};
+use core::{
+    marker::PhantomData,
+    mem::ManuallyDrop,
+    ops::Deref,
+    ptr::NonNull, //
+};
 
 /// Types that are _always_ reference counted.
 ///