powerpc/pseries/mobility: don't error on absence of ibm, update-nodes

Treat the absence of the ibm,update-nodes function as benign instead
of reporting an error. If the platform does not provide that facility,
it's not a problem for Linux.
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201207215200.1785968-8-nathanl@linux.ibm.com

arch/powerpc/platforms/pseries/mobility.c

@@ -261,7 +261,7 @@ int pseries_devicetree_update(s32 scope)
 
 	update_nodes_token = rtas_token("ibm,update-nodes");
 	if (update_nodes_token == RTAS_UNKNOWN_SERVICE)
-		return -EINVAL;
+		return 0;
 
 	rtas_buf = kzalloc(RTAS_DATA_BUF_SIZE, GFP_KERNEL);
 	if (!rtas_buf)