drm/bridge: tc358767: fix 1-lane behavior

Use drm_dp_channel_eq_ok helper

Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Andrey Gusakov <andrey.gusakov@cogentembedded.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1510073785-16108-7-git-send-email-andrey.gusakov@cogentembedded.com