drm: Fix error handling in drm_connector_register

When debugfs or sysfs registration failed, we failed to clean up the
idr registration. Reorder to fix this.

Cc: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1462539302-27764-1-git-send-email-daniel.vetter@ffwll.ch