drm/i915/mst: Debug log connector name in destroy_connector()

Print connector name in destroy_connect() and this doesn't add any extra
lines to dmesg. The debug macro has been moved before the unregister
call so that we don't lose the connector name and id.

Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170918222141.4674-1-dhinakaran.pandiyan@intel.com