Claude review: gpu: nova-core: replace ARef<Device> with &'bound Device in SysmemFlush

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

Straightforward simplification now that `SysmemFlush<'sys>` has a lifetime parameter.

```rust
-    device: ARef<device::Device>,
+    device: &'sys device::Device,
```

And in `register()`:

```rust
-        dev: &device::Device<device::Bound>,
+        dev: &'sys device::Device<device::Bound>,
```

With:

```rust
-            device: dev.into(),
+            device: dev,
```

**One observation:** The `device` field type is `&'sys device::Device` (unparameterized), but the `register()` function takes `&'sys device::Device<device::Bound>`. The assignment `device: dev` works because `device::Device<device::Bound>` derefs to `device::Device` (the unparameterized form). This is an implicit coercion that's standard in the kernel Rust device model — just noting it for clarity.

The `ARef` import removal is clean. No issues found.

---
Generated by Claude Code Patch Reviewer