drm/tests: hdmi: Switch to drm_atomic_get_new_connector_state() where possible

drm/tests: hdmi: Switch to drm_atomic_get_new_connector_state() where possible

Replace the calls to drm_atomic_get_connector_state() with
drm_atomic_get_new_connector_state() for cases which do not require
allocating the connector state, e.g. after drm_atomic_check_only() when
the intent is to only read the new connector state.

The rational is to avoid the need to handle the potential EDEADLK error
returned by the former helper, which would require restarting the entire
atomic sequence.

Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Link: https://lore.kernel.org/r/20250527-hdmi-conn-yuv-v5-13-74c9c4a8ac0c@collabora.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>