Claude review: drm: fix dead default for DRM_TTM_KUNIT_TEST

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

Patch Review

**Correctness:** The patch correctly removes the `default n` line. After removal, the remaining `default KUNIT_ALL_TESTS` will properly take effect — defaulting to `y` when `KUNIT_ALL_TESTS=y`, and to `n` otherwise (since Kconfig tristates default to `n` when no default matches).

**Commit message:** Clear and well-written. Correctly identifies the problem (shadowed default), references the tool that found it, and includes a proper `Fixes:` tag pointing to commit `e3912d09bf8d ("drm/ttm: Introduce KUnit test")`.

**Style note:** After this patch, the `default KUNIT_ALL_TESTS` line (currently line 94 in the tree) sits after the `select` statements, which matches the ordering used by `DRM_KUNIT_TEST` and `DRM_SCHED_KUNIT_TEST` in the same file. No issues there.

**One minor observation:** The ordering convention in this file for the other entries places `default KUNIT_ALL_TESTS` *after* the `select` blocks. The patched result preserves that convention, which is good.

Reviewed-by assessment: This patch is correct and ready to apply.

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