drm/bridge: tc358775: Fix drm_of_get_data_lanes_count_ep conversion

Initialize dsi_lanes to -1, so that in case the endpoint is missing,
probe would fail as it did before the conversion, instead of depending
on uninitialized variable and thus undefined behavior.

Fixes: 56426faa ("drm/bridge: tc358775: Convert to drm_of_get_data_lanes_count_ep")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Marek Vasut <marex@denx.de>
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
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220612132152.91052-2-marex@denx.de