drm: qxl: Atomic phase 1: Don't unpin primary when disabling crtc

In the qxl atomic model, the primary doesn't stay pinned all the time,
instead it is only pinned/unpinned between prepare_fb and cleanup_fb.
So, we no longer need a final unpin of the primary framebuffer when
disabling the crtc.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170227204328.18761-9-krisman@collabora.co.uk


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