The drm_of_lvds_get_data_mapping() returns either negative value on
error or MEDIA_BUS_FMT_* otherwise. The check for 'ret' would also
catch the positive case of MEDIA_BUS_FMT_* and lead to probe failure
every time 'data-mapping' DT property is specified.

Fixes: 7c4dd0a2 ("drm: of: Add drm_of_lvds_get_data_mapping")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
To: dri-devel@lists.freedesktop.org
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220801125419.167562-1-marex@denx.de