Fix an oops in i915_gem_retire_requests()

dev_priv->hw_status_page can be NULL, if i915_gem_retire_requests()
is called from i915_gem_busy_ioctl().

Signed-off-by Karsten Wiese <fzu@wemgehoertderstaat.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/gpu/drm/i915/i915_gem.c

@@ -1051,6 +1051,9 @@ i915_gem_retire_requests(struct drm_device *dev)
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	uint32_t seqno;
 
+	if (!dev_priv->hw_status_page)
+		return;
+
 	seqno = i915_get_gem_seqno(dev);
 
 	while (!list_empty(&dev_priv->mm.request_list)) {