drm/tests: hdmi: rename connector creation function

As pointed out by Maxime, the drm_atomic_helper_connector_hdmi_init()
isn't a good name for a function inside KUnit tests. Rename it to
drm_kunit_helper_connector_hdmi_init().

Suggested-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241130-hdmi-mode-valid-v5-2-742644ec3b1f@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>