drm/i915/sdvo: clean up connectors on intel_sdvo_init() failures

Any failures in intel_sdvo_init() after the intel_sdvo_setup_output() call
left behind ghost connectors, attached (with a dangling pointer) to the
sdvo that has been cleaned up and freed. Properly destroy any connectors
attached to the encoder.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=46381


CC: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Cc: stable@vger.kernel.org
Tested-by:  <bjo@nord-west.org>
[danvet: added a comment to explain why we need to clean up connectors
even when sdvo_output_setup fails.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>