drm/bridge: lontium-lt9611: drop atomic_check() callback

As drm_bridge_connector now provides atomic_check() implementation which
calls drm_atomic_helper_connector_hdmi_check(), drop the duplicating
callback from the bridge driver.

Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241210-bridge_hdmi_check-v1-3-a8fdd8c5afa5@linaro.org


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