ftrace: fix merge

Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/ftrace.h

@@ -122,7 +122,7 @@ static inline void tracer_disable(void)
 # define trace_preempt_off(a0, a1)		do { } while (0)
 #endif
 
-#ifdef CONFIG_CONTEXT_SWITCH_TRACER
+#ifdef CONFIG_TRACING
 extern void
 ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3);
 #else