drm/i915: Unpin the ringbuffer if we fail to ioremap it.

A missing unpin on the error path.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/gpu/drm/i915/i915_gem.c

@@ -3159,6 +3159,7 @@ i915_gem_init_ringbuffer(struct drm_device *dev)
 	if (ring->map.handle == NULL) {
 		DRM_ERROR("Failed to map ringbuffer.\n");
 		memset(&dev_priv->ring, 0, sizeof(dev_priv->ring));
+		i915_gem_object_unpin(obj);
 		drm_gem_object_unreference(obj);
 		return -EINVAL;
 	}