drm/bridge: ti-sn65dsi83: Handle dsi_lanes == 0 as invalid

Handle empty data-lanes = < >; property, which translates to
dsi_lanes = 0 as invalid.

Fixes: ceb515ba ("drm/bridge: ti-sn65dsi83: Add TI SN65DSI83 and SN65DSI84 driver")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Jonas Karlman <jonas@kwiboo.se>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Robert Foss <robert.foss@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220518233844.248504-1-marex@denx.de