drm/omap: dss: Handle DPI and SDI port initialization failures

The dpi_init_port() and sdi_init_port() functions can return errors but
their return value is ignored. This prevents both probe failures and
probe deferral from working correctly. Propagate the errors up the call
stack.

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>