drm/i915: fix WC mapping in non-GEM i915 code.

[airlied - taken from mailing list posting]
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/i915_dma.c

@@ -202,7 +202,7 @@ static int i915_initialize(struct drm_device * dev, drm_i915_init_t * init)
 		dev_priv->ring.map.flags = 0;
 		dev_priv->ring.map.mtrr = 0;
 
-		drm_core_ioremap(&dev_priv->ring.map, dev);
+		drm_core_ioremap_wc(&dev_priv->ring.map, dev);
 
 		if (dev_priv->ring.map.handle == NULL) {
 			i915_dma_cleanup(dev);