drm: handle compact dma scatter lists in drm_clflush_sg()

So far the assumption was that each scatter list entry contains a single
page. This might not hold in the future, when we'll introduce compact
scatter lists, so prepare for this here.

Reference: http://www.spinics.net/lists/dri-devel/msg33917.html
Signed-off-by: Imre Deak <imre.deak@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_cache.c

@@ -105,12 +105,11 @@ drm_clflush_sg(struct sg_table *st)
 {
 #if defined(CONFIG_X86)
 	if (cpu_has_clflush) {
-		struct scatterlist *sg;
-		int i;
+		struct sg_page_iter sg_iter;
 
 		mb();
-		for_each_sg(st->sgl, sg, st->nents, i)
-			drm_clflush_page(sg_page(sg));
+		for_each_sg_page(st->sgl, &sg_iter, st->nents, 0)
+			drm_clflush_page(sg_iter.page);
 		mb();
 
 		return;