Claude review: drm/tegra: fbdev: Calculate buffer geometry with format helpers

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

Patch Review

**Status: Good, one minor style nit**

Replaces the manual `bytes_per_pixel` / pitch / size calculation with the standard DRM format helpers:

```c
fourcc = drm_mode_legacy_fb_format(sizes->surface_bpp, sizes->surface_depth);
format = drm_get_format_info(drm, fourcc, DRM_FORMAT_MOD_LINEAR);
pitch = round_up(drm_format_info_min_pitch(format, 0, sizes->surface_width),
		 tegra->pitch_align);
size = ALIGN(pitch * sizes->surface_height, PAGE_SIZE);
```

The `DRM_FORMAT_MOD_LINEAR` argument is equivalent to the old zero-initialized `cmd.modifier[0]`. The added `PAGE_SIZE` alignment on size is an improvement — `tegra_bo_create` will round up anyway, and this makes the allocation explicit.

Using `bo->gem.size` instead of the locally calculated `size` for `screen_size` / `smem_len` is correct — it reflects the actual allocated buffer size after any internal alignment by the GEM allocator:

```c
-	info->screen_size = size;
+	info->screen_size = bo->gem.size;
```

**Minor nit:** Variable declarations are not in reverse-christmas-tree order — `const struct drm_format_info *format` is declared after the shorter variables. Very minor and not worth blocking.

---
Generated by Claude Code Patch Reviewer