Claude review: drm/nouveau: tegra: Explicitly specify PMC instance to use

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

Patch Review

Adds `struct tegra_pmc *pmc` to `nvkm_device_tegra` and calls `devm_tegra_pmc_get()` in `nvkm_device_tegra_new()`. The error path uses `goto free`, which is correct for where the lookup is inserted (after clk_pwr, before dma_set_mask).

Minor observation: unlike other patches that use `dev_err_probe()`, this one silently returns the error code on PMC lookup failure:

```c
	tdev->pmc = devm_tegra_pmc_get(&pdev->dev);
	if (IS_ERR(tdev->pmc)) {
		ret = PTR_ERR(tdev->pmc);
		goto free;
	}
```

This is inconsistent with the other patches but matches the existing error style in this function (e.g., `clk_pwr` above it). Acceptable, but a `dev_err_probe()` would be more helpful for debugging `-EPROBE_DEFER`.

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