drm/bridge: lt8912: Convert to drm_of_get_data_lanes_count_ep

drm/bridge: lt8912: Convert to drm_of_get_data_lanes_count_ep

Convert driver to use this new helper to standardize
OF "data-lanes" parsing.

Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Adrien Grassein <adrien.grassein@gmail.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Robert Foss <robert.foss@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
To: dri-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20220524010522.528569-4-marex@denx.de