drm/tests: hdmi: Fix recursive locking

The find_preferred_mode() functions takes the mode_config mutex, but due
to the order most tests have, is called with the crtc_ww_class_mutex
taken. This raises a warning for a circular dependency when running the
tests with lockdep.

Reorder the tests to call find_preferred_mode before the acquire context
has been created to avoid the issue.

Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20250129-test-kunit-v2-4-fe59c43805d5@kernel.org


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