drm/i915: rename intel_dp_destroy to intel_dp_connector_destroy

Because it's the function that destroys the connector, not the
encoder. And we already have intel_dp_encoder_destroy.

This has annoyed me for a long time.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Zoltan Nyul <zoltan.nyul@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>