drm/cirrus: fix connector leak at unload

This fixes an '*ERROR* connector VGA-2 leaked!' splat at driver unload.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20190111140242.29002-1-robdclark@gmail.com



[ kraxel: adapt to commit "c2d88e06 drm: Move the legacy kms
          disable_all helper to crtc helpers" ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>