tracing/boot: Fix to check the histogram control param is a leaf node

Since xbc_node_find_child() doesn't ensure the returned node
is a leaf node (key-value pair or do not have subkeys),
use xbc_node_find_value to ensure the histogram control
parameter is a leaf node in trace_boot_compose_hist_cmd().

Link: https://lkml.kernel.org/r/163119459059.161018.18341288218424528962.stgit@devnote2

Fixes: e66ed86c ("tracing/boot: Add per-event histogram action options")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_boot.c

@@ -385,11 +385,11 @@ trace_boot_compose_hist_cmd(struct xbc_node *hnode, char *buf, size_t size)
 	}
 
 	/* Histogram control attributes (mutual exclusive) */
-	if (xbc_node_find_child(hnode, "pause"))
+	if (xbc_node_find_value(hnode, "pause", NULL))
 		append_printf(&buf, end, ":pause");
-	else if (xbc_node_find_child(hnode, "continue"))
+	else if (xbc_node_find_value(hnode, "continue", NULL))
 		append_printf(&buf, end, ":continue");
-	else if (xbc_node_find_child(hnode, "clear"))
+	else if (xbc_node_find_value(hnode, "clear", NULL))
 		append_printf(&buf, end, ":clear");
 
 	/* Histogram handler and actions */