drm: omapdrm: venc: Return error code on OF parsing failure

The venc_probe_of() function has an error cleanup path that returns
success instead of an error code. Fix it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>