Claude review: drm/amdgpu: switch XGMI sysfs show helpers to sysfs_emit_at()

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

Patch Review

**Positive aspects:**

1. Fixes a real (albeit likely benign in practice) undefined behavior issue where the old code passes `buf` as both output buffer and `%s` format argument in `sysfs_emit(buf, "%s\n", buf)`.
2. The conversion to `sysfs_emit_at()` is the correct modern kernel API for building up sysfs output incrementally.
3. Matches the existing style of `amdgpu_xgmi_show_connected_port_num()` at line 505 of the same file, which already uses `sysfs_emit_at()` with a `size` offset variable.

**Minor concern:**

The return value calculation on the final line:

```c
return offset + sysfs_emit_at(buf, offset, "\n");
```

This works correctly — `offset` holds the bytes written so far, and `sysfs_emit_at()` returns the number of bytes written for the newline (1), so the total returned is the full length. However, there is an edge case: if `sysfs_emit_at()` were to return a negative error value, this addition would produce an incorrect result. In practice, `sysfs_emit_at()` only returns negative if `offset` is already beyond `PAGE_SIZE`, which won't happen here with a reasonable `num_nodes` count. The neighboring `amdgpu_xgmi_show_connected_port_num()` uses the same `size +=` pattern, so this is consistent.

**Overall:** The patch is clean, correct, and well-scoped. No issues that would block merging.

Reviewed-by: looks good to me.

---
Generated by Claude Code Patch Reviewer