drm/i915/ringbuffer: Disable the ringbuffer on cleanup.

void intel_cleanup_ring_buffer(struct intel_ring_buffer *ring)

{

	struct drm_i915_private *dev_priv;

	int ret;

	if (ring->gem_object == NULL)

		return;

	/* Disable the ring buffer. The ring must be idle at this point */

	dev_priv = ring->dev->dev_private;

	ret = intel_wait_ring_buffer(ring, ring->size - 8);

	I915_WRITE_CTL(ring, 0);

	drm_core_ioremapfree(&ring->map, ring->dev);

	i915_gem_object_unpin(ring->gem_object);