drm/tests: hdmi: Reorder DRM entities variables assignment

The tests all deviate slightly in how they assign their local pointers
to DRM entities. This makes refactoring pretty difficult, so let's just
move the assignment as soon as the entities are allocated.

Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20250129-test-kunit-v2-3-fe59c43805d5@kernel.org


Signed-off-by: Maxime Ripard <mripard@kernel.org>