drm: of: Fix double-free bug

Fix double-free bug in the error path.

Fixes: 65290075

 ("drm: of: Add drm_of_lvds_get_dual_link_pixel_order")
Reported-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1595502654-40595-1-git-send-email-biju.das.jz@bp.renesas.com