Claude review: drm/panthor: Use the drm_dev_access guard

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

Patch Review

Clean application of the drm_dev_access guard from patch 3. Several patterns emerge:

**IOCTL paths using `ACQUIRE`/`ACQUIRE_ERR`:**
```c
ACQUIRE(drm_dev_access, dev_guard)(ddev);
if (ACQUIRE_ERR(drm_dev_access, &dev_guard))
    return -ENODEV;
```
This is verbose compared to the old `if (!drm_dev_enter(ddev, &cookie)) return -ENODEV;` — it's 2 lines vs 2 lines but with longer names. The payoff is removing the `drm_dev_exit(cookie)` and any gotos to it.

**`panthor_device_resume()` — `scoped_cond_guard` with `ret = 0` fallthrough:**
```c
scoped_cond_guard(drm_dev_access, ret = 0, &ptdev->base) {
```
When `drm_dev_enter` fails (device unplugged), `ret` is set to 0 and the block is skipped. This is correct — the original code also just skipped the block with `drm_dev_enter()` returning false.

**`panthor_device_suspend()` — `scoped_guard` without error action:**
```c
scoped_guard(drm_dev_access, &ptdev->base) {
```
Using `scoped_guard` (not `scoped_cond_guard`) means if `drm_dev_enter` fails, the block is silently skipped. The original code had the same behavior (`if (...drm_dev_enter(...))`). This is correct for suspend — if the device is already unplugged, skipping teardown is fine.

**`panthor_vm_active()` simplification:**
The conversion from:
```c
scoped_guard(mutex, &vm->op_lock) {
    guard(mutex)(&ptdev->mmu->as.slots_lock);
    ret = panthor_vm_active_locked(vm);
}
```
to:
```c
guard(mutex)(&vm->op_lock);
guard(mutex)(&ptdev->mmu->as.slots_lock);
return panthor_vm_active_locked(vm);
```
This is functionally equivalent since we're at the end of the function either way. Cleaner.

---
Generated by Claude Code Patch Reviewer