kernel/stop_machine.c: fix unused variable warning

kernel/stop_machine.c: In function `cpu_stopper_thread':
kernel/stop_machine.c:265: warning: unused variable `ksym_buf'

ksym_buf[] is unused if WARN_ON() is a no-op.
Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/stop_machine.c

@@ -262,7 +262,7 @@ static int cpu_stopper_thread(void *data)
 		cpu_stop_fn_t fn = work->fn;
 		void *arg = work->arg;
 		struct cpu_stop_done *done = work->done;
-		char ksym_buf[KSYM_NAME_LEN];
+		char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
 
 		__set_current_state(TASK_RUNNING);