Claude review: drm/panfrost: Drop redundant optional clock checks in runtime PM

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

Patch Review

The commit message correctly explains that `clk_enable(NULL)` returns 0 and `clk_disable(NULL)` is a no-op, so the `if (pfdev->bus_clock)` guards are unnecessary.

**Observation:** This patch only removes the NULL checks in `panfrost_device_runtime_resume()` and `panfrost_device_runtime_suspend()` (the `GPU_PM_RT` path), but leaves identical redundant checks in `panfrost_device_resume()` and `panfrost_device_suspend()` (the `GPU_PM_CLK_DIS` path):

```c
// panfrost_device_resume() still has:
if (pfdev->bus_clock) {
    ret = clk_enable(pfdev->bus_clock);

// panfrost_device_suspend() still has:
if (pfdev->bus_clock)
    clk_disable(pfdev->bus_clock);
```

For consistency, it would be cleaner to also drop those guards in the same patch. Not a blocking issue since the `GPU_PM_CLK_DIS` path is a separate code path, but it would be more complete.

The change itself is correct.

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