drm/nv50: fix stability issue on NV86.

Confirmed to fix random hangs while running all Unegine demos on NV86.
Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nv50_grctx.c

@@ -601,7 +601,7 @@ nv50_graph_construct_mmio(struct nouveau_grctx *ctx)
 					gr_def(ctx, offset + 0x1c, 0x00880000);
 					break;
 				case 0x86:
-					gr_def(ctx, offset + 0x1c, 0x008c0000);
+					gr_def(ctx, offset + 0x1c, 0x018c0000);
 					break;
 				case 0x92:
 				case 0x96: