rust: driver-core: Update ARef and AlwaysRefCounted imports from sync::aref

rust: driver-core: Update ARef and AlwaysRefCounted imports from sync::aref

Update call sites in the driver-core files and its related samples
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: https://github.com/Rust-for-Linux/linux/issues/1173
Signed-off-by: Shankari Anand <shankari.ak0208@gmail.com>
Link: https://lore.kernel.org/r/20250814104615.355106-1-shankari.ak0208@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>