drm/i915/dsi: Call drm_connector_cleanup on vlv_dsi_init error exit path

If we exit vlv_dsi_init() because we failed to find a fixed_mode, then
we've already called drm_connector_init() and we should call
drm_connector_cleanup() to unregister the connector object.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190524163518.17545-1-hdegoede@redhat.com