drm/exynos: mixer: simplify mixer_graph_buffer()

DRM core already checks in drm_atomic_plane_check() if the
pixelformat is valid. Hence we can collapse the default case
of the switch statement with the XRGB8888 case.

No functional change.
Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_mixer.c

@@ -606,12 +606,9 @@ static void mixer_graph_buffer(struct mixer_context *ctx,
 
 	case DRM_FORMAT_XRGB8888:
 	case DRM_FORMAT_ARGB8888:
+	default:
 		fmt = MXR_FORMAT_ARGB8888;
 		break;
-
-	default:
-		DRM_DEBUG_KMS("pixelformat unsupported by mixer\n");
-		return;
 	}
 
 	/* ratio is already checked by common plane code */