drm: make sure vblank interrupts are disabled at DPMS time

When we call drm_vblank_off() at DPMS off time (to wake any clients so
they don't hang) we need to make sure interrupts are actually disabled.
If drm_vblank_off() gets called before the vblank usage timer expires,
it'll prevent the timer from disabling interrupts since it also clears
the vblank_enabled flag for the pipe.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_irq.c

@@ -475,6 +475,7 @@ void drm_vblank_off(struct drm_device *dev, int crtc)
 	unsigned long irqflags;
 
 	spin_lock_irqsave(&dev->vbl_lock, irqflags);
+	dev->driver->disable_vblank(dev, crtc);
 	DRM_WAKEUP(&dev->vbl_queue[crtc]);
 	dev->vblank_enabled[crtc] = 0;
 	dev->last_vblank[crtc] = dev->driver->get_vblank_counter(dev, crtc);