Label kthread_create() with printf attribute tag.

Obvious misc patch been in my queue (& linux-next) for over a cycle.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kthread.h

@@ -6,7 +6,8 @@
 
 struct task_struct *kthread_create(int (*threadfn)(void *data),
 				   void *data,
-				   const char namefmt[], ...);
+				   const char namefmt[], ...)
+	__attribute__((format(printf, 3, 4)));
 
 /**
  * kthread_run - create and wake a thread.