powerpc/powernv: add missing of_node_put() in opal_export_attrs()

After using 'np' returned by of_find_node_by_path(), of_node_put()
need be called to decrease the refcount.

Fixes: 11fe909d23 ("powerpc/powernv: Add OPAL exports attributes to sysfs")
Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220906141703.118192-1-zhengyongjun3@huawei.com

arch/powerpc/platforms/powernv/opal.c

@@ -892,6 +892,7 @@ static void opal_export_attrs(void)
 	kobj = kobject_create_and_add("exports", opal_kobj);
 	if (!kobj) {
 		pr_warn("kobject_create_and_add() of exports failed\n");
+		of_node_put(np);
 		return;
 	}