ftrace: Copy ftrace_graph_filter boot param using strlcpy

We are using strncpy in the wrong way to copy the ftrace_graph_filter
boot param because we pass the buffer size instead of the max string
size it can contain (buffer size - 1). The end result might not be
NULL terminated as we are abusing the max string size.

Lets use strlcpy() instead.
Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -2293,7 +2293,7 @@ __setup("ftrace_filter=", set_ftrace_filter);
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 static int __init set_graph_function(char *str)
 {
-	strncpy(ftrace_graph_buf, str, FTRACE_FILTER_SIZE);
+	strlcpy(ftrace_graph_buf, str, FTRACE_FILTER_SIZE);
 	return 1;
 }
 __setup("ftrace_graph_filter=", set_graph_function);