drm/amdgpu: skip VM inv eng assignment for mes ring

Statically allocated VM inv eng of gfxhub on sienna_cichlid is used up.
Also VM inv eng is no need for mes ring.

Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c

@@ -357,6 +357,9 @@ int amdgpu_gmc_allocate_vm_inv_eng(struct amdgpu_device *adev)
 		ring = adev->rings[i];
 		vmhub = ring->funcs->vmhub;
 
+		if (ring == &adev->mes.ring)
+			continue;
+
 		inv_eng = ffs(vm_inv_engs[vmhub]);
 		if (!inv_eng) {
 			dev_err(adev->dev, "no VM inv eng for ring %s\n",