drm/nvc0: enable protection of system-use-only structures in vm

Somehow missed this in the original merge of the nvc0 code.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nv50_instmem.c b/drivers/gpu/drm/nouveau/nv50_instmem.c
index 2e1b1cd..ea00418 100644
--- a/drivers/gpu/drm/nouveau/nv50_instmem.c
+++ b/drivers/gpu/drm/nouveau/nv50_instmem.c
@@ -332,8 +332,11 @@
 	gpuobj->vinst = node->vram->offset;
 
 	if (gpuobj->flags & NVOBJ_FLAG_VM) {
-		ret = nouveau_vm_get(dev_priv->chan_vm, size, 12,
-				     NV_MEM_ACCESS_RW | NV_MEM_ACCESS_SYS,
+		u32 flags = NV_MEM_ACCESS_RW;
+		if (!(gpuobj->flags & NVOBJ_FLAG_VM_USER))
+			flags |= NV_MEM_ACCESS_SYS;
+
+		ret = nouveau_vm_get(dev_priv->chan_vm, size, 12, flags,
 				     &node->chan_vma);
 		if (ret) {
 			vram->put(dev, &node->vram);