ftrace: Hide cached module code for !CONFIG_MODULES

When modules are disabled, we get a harmless build warning:

kernel/trace/ftrace.c:4051:13: error: 'process_cached_mods' defined but not used [-Werror=unused-function]

This adds the same #ifdef around the new code that exists around
its caller.

Link: http://lkml.kernel.org/r/20170710084413.1820568-1-arnd@arndb.de

Fixes: d7fbf8df7c ("ftrace: Implement cached modules tracing on module load")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -3978,6 +3978,7 @@ static int
 ftrace_set_regex(struct ftrace_ops *ops, unsigned char *buf, int len,
 		 int reset, int enable);
 
+#ifdef CONFIG_MODULES
 static void process_mod_list(struct list_head *head, struct ftrace_ops *ops,
 			     char *mod, bool enable)
 {
@@ -4068,6 +4069,7 @@ static void process_cached_mods(const char *mod_name)
 
 	kfree(mod);
 }
+#endif
 
 /*
  * We register the module command as a template to show others how