powerpc/numa: Fix OF node refcounting bug

The form affinity for NUMA is set to 1 if the firmware supports
OPAL. Otherwise, we have to retrieve that from OF node "/chosen".
For the latter case, OF node "/chosen" reference count was never
decreased.
Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/mm/numa.c

@@ -340,6 +340,8 @@ static int __init find_min_common_depth(void)
 				dbg("Using form 1 affinity\n");
 				form1_affinity = 1;
 			}
+
+			of_node_put(chosen);
 		}
 	}