tracing/boot: Fix to loop on only subkeys

Since the commit e5efaeb ("bootconfig: Support mixing
a value and subkeys under a key") allows to co-exist a value
node and key nodes under a node, xbc_node_for_each_child()
is not only returning key node but also a value node.
In the boot-time tracing using xbc_node_for_each_child() to
iterate the events, groups and instances, but those must be
key nodes. Thus it must use xbc_node_for_each_subkey().

Link: https://lkml.kernel.org/r/163112988361.74896.2267026262061819145.stgit@devnote2

Fixes: e5efaeb ("bootconfig: Support mixing a value and subkeys under a key")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Author: mhiramat

kernel/trace/trace_boot.c

@@ -522,14 +522,14 @@ trace_boot_init_events(struct trace_array *tr, struct xbc_node *node)
 	if (!node)
 		return;
 	/* per-event key starts with "event.GROUP.EVENT" */
-	xbc_node_for_each_child(node, gnode) {
+	xbc_node_for_each_subkey(node, gnode) {
 		data = xbc_node_get_data(gnode);
 		if (!strcmp(data, "enable")) {
 			enable_all = true;
 			continue;
 		}
 		enable = false;
-		xbc_node_for_each_child(gnode, enode) {
+		xbc_node_for_each_subkey(gnode, enode) {
 			data = xbc_node_get_data(enode);
 			if (!strcmp(data, "enable")) {
 				enable = true;
@@ -625,7 +625,7 @@ trace_boot_init_instances(struct xbc_node *node)
 	if (!node)
 		return;
 
-	xbc_node_for_each_child(node, inode) {
+	xbc_node_for_each_subkey(node, inode) {
 		p = xbc_node_get_data(inode);
 		if (!p || *p == '\0')
 			continue;