drm/imx: parallel-display: Accept drm_of_find_panel_or_bridge failure

The parallel panel driver should continue to work without having an
endpoint linking to an panel in DT for backwards compatibility.
With the recent switch to drm_of_find_panel_or_bridge, an absent
panel results in a failure with -ENODEV error return code. To restore
the old behaviour, ignore the -ENODEV return code.

Reported-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Fixes: ebc94461 ("drm: convert drivers to use drm_of_find_panel_or_bridge")
Tested-by: Chris Healy <cphealy@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>