Claude review: drm/vblank: Add some debugging trace events

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

Patch Review

Straightforward tracing additions. Useful for debugging the new deferred path.

**Minor issues:**

1. Format string mismatch in `drm_vblank_get_put_template`:
```c
TP_STRUCT__entry(
    __field(int, refcount)
),
TP_printk(
    "crtc=%d, refcount=%u",    // %u for signed int
```
`refcount` is declared as `int` but printed with `%u`. Use `%d` for consistency.

2. The `drm_vblank_put` trace point reads `atomic_read(&vblank->refcount)` **before** `atomic_dec_and_test()`:
```c
trace_drm_vblank_put(pipe, atomic_read(&vblank->refcount));

/* Last user schedules interrupt disable */
if (!atomic_dec_and_test(&vblank->refcount))
    return;
```
The comment "put's refcount not sync'd using vbl_lock, use for debugging purposes only" is appropriate, but the trace shows the refcount *before* the put, not after. This is fine for debugging but could confuse readers expecting the post-decrement value.

3. The `trace_drm_vblank_get` placement is before the `atomic_add_return`, so it also shows the pre-increment refcount, which is at least consistent with the put trace.

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Generated by Claude Code Patch Reviewer