drm/i915: Don't kick-off hangcheck after a DRI interrupt

Hangcheck and error recovery is only used by GEM.

Reported-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index b8e509a..f0c87bd 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -348,8 +348,12 @@
 			struct intel_ring_buffer *ring)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	u32 seqno = ring->get_seqno(ring);
+	u32 seqno;
 
+	if (ring->obj == NULL)
+		return;
+
+	seqno = ring->get_seqno(ring);
 	trace_i915_gem_request_complete(dev, seqno);
 
 	ring->irq_seqno = seqno;