irqchip/gic-v3: Fix ppi-partitions lookup

Fix child-node lookup during initialisation, which ended up searching
the whole device tree depth-first starting at the parent rather than
just matching on its children.

To make things worse, the parent gic node was prematurely freed, while
the ppi-partitions node was leaked.

Fixes: e3825ba1af ("irqchip/gic-v3: Add support for partitioned PPIs")
Cc: stable <stable@vger.kernel.org>     # 4.7
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

drivers/irqchip/irq-gic-v3.c

@@ -1103,18 +1103,18 @@ static void __init gic_populate_ppi_partitions(struct device_node *gic_node)
 	int nr_parts;
 	struct partition_affinity *parts;
 
-	parts_node = of_find_node_by_name(gic_node, "ppi-partitions");
+	parts_node = of_get_child_by_name(gic_node, "ppi-partitions");
 	if (!parts_node)
 		return;
 
 	nr_parts = of_get_child_count(parts_node);
 
 	if (!nr_parts)
-		return;
+		goto out_put_node;
 
 	parts = kzalloc(sizeof(*parts) * nr_parts, GFP_KERNEL);
 	if (WARN_ON(!parts))
-		return;
+		goto out_put_node;
 
 	for_each_child_of_node(parts_node, child_part) {
 		struct partition_affinity *part;
@@ -1181,6 +1181,9 @@ static void __init gic_populate_ppi_partitions(struct device_node *gic_node)
 
 		gic_data.ppi_descs[i] = desc;
 	}
+
+out_put_node:
+	of_node_put(parts_node);
 }
 
 static void __init gic_of_setup_kvm_info(struct device_node *node)