drm/imx: parallel-display: move panel/bridge detection to fail early

We do some string parsing and string comparison in front of
drm_of_find_panel_or_bridge(). All this work is useless if the call
fails. Move drm_of_find_panel_or_bridge() infront of the parsing work to
fail early.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>