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/r300.c b/drivers/gpu/drm/radeon/r300.c
index 6ec86fc..ad0a0e6 100644
--- a/drivers/gpu/drm/radeon/r300.c
+++ b/drivers/gpu/drm/radeon/r300.c
@@ -1043,7 +1043,7 @@
 		break;
 	case 0x4d1c:
 		/* ZB_BW_CNTL */
-		track->fastfill = !!(idx_value & (1 << 2));
+		track->zb_cb_clear = !!(idx_value & (1 << 5));
 		break;
 	case 0x4e04:
 		/* RB3D_BLENDCNTL */