drm/bridge: tc358767: fix probe without attached output node

The output node of the TC358767 is only used if another bridge is chained
behind it. Panels attached to the TC358767 can be detected using the usual
DP AUX probing. This restores the old behavior of ignoring the output if
no endpoint is found.

Fixes: ebc94461 (drm: convert drivers to use drm_of_find_panel_or_bridge)
CC: stable@vger.kernel.org
Acked-by: Andrey Gusakov <andrey.gusakov@cogentembedded.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20170710124125.9019-1-l.stach@pengutronix.de