Claude review: media: renesas: vsp1: Use spinlock guards

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

Patch Review

Same pattern as patch 5 but for spinlocks. Converts `spin_lock_irqsave()`/`spin_unlock_irqrestore()` and `spin_lock_irq()`/`spin_unlock_irq()` pairs to `guard(spinlock_irqsave)()` and `guard(spinlock_irq)()` respectively. Affected: `vsp1_dl.c`, `vsp1_histo.c`, `vsp1_pipe.c`, `vsp1_video.c`, `vsp1_wpf.c`.

Notable: the `vsp1_dlm_irq_frame_end()` conversion replaces `goto done` at the end-of-function unlock with direct `return flags`, since `guard(spinlock)` handles the unlock. Clean refactoring.

The `vsp1_pipeline_stopped()` conversion is particularly nice, reducing 5 lines to 2:

```c
guard(spinlock_irqsave)(&pipe->irqlock);
return pipe->state == VSP1_PIPELINE_STOPPED;
```

**All correct.**

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