drivers: gpu: Update ARef imports from sync::aref

drivers: gpu: Update ARef imports from sync::aref

Update call sites to import `ARef` 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>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20251123092438.182251-3-shankari.ak0208@gmail.com
[aliceryhl: keep trailing // at last import]
Signed-off-by: Alice Ryhl <aliceryhl@google.com>