drm/nv50-/fbcon: move 2d class to subchannel 3

Kepler GRAPH has (well, sorta) fixed subchannel<->class assignments, make
this match up to keep it happy without trapping.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_dma.h

@@ -50,8 +50,8 @@ void nv50_dma_push(struct nouveau_channel *, struct nouveau_bo *,
 enum {
 	NvSubM2MF	= 0,
 	NvSubSw		= 1,
-	NvSub2D		= 2,
 	NvSubCtxSurf2D  = 2,
+	NvSub2D		= 3,
 	NvSubGdiRect    = 3,
 	NvSubImageBlit  = 4
 };