drm/radeon/kms: r300 fix CS checker to allow zbuffer-only fastfill

Signed-off-by: Marek Olšák <maraeo@gmail.com>
diff --git a/drivers/gpu/drm/radeon/r100.c b/drivers/gpu/drm/radeon/r100.c
index c06207e..e302579 100644
--- a/drivers/gpu/drm/radeon/r100.c
+++ b/drivers/gpu/drm/radeon/r100.c
@@ -2974,7 +2974,7 @@
 
 	for (i = 0; i < track->num_cb; i++) {
 		if (track->cb[i].robj == NULL) {
-			if (!(track->fastfill || track->color_channel_mask ||
+			if (!(track->zb_cb_clear || track->color_channel_mask ||
 			      track->blend_read_enable)) {
 				continue;
 			}