tracing: remove set but not used variable 'buffer'

kernel/trace/trace_events_inject.c: In function trace_inject_entry:
kernel/trace/trace_events_inject.c:20:22: warning: variable buffer set but not used [-Wunused-but-set-variable]

It is never used, so remove it.

Link: http://lkml.kernel.org/r/20191207034409.25668-1-yuehaibing@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_inject.c

@@ -17,12 +17,10 @@ static int
 trace_inject_entry(struct trace_event_file *file, void *rec, int len)
 {
 	struct trace_event_buffer fbuffer;
-	struct ring_buffer *buffer;
 	int written = 0;
 	void *entry;
 
 	rcu_read_lock_sched();
-	buffer = file->tr->trace_buffer.buffer;
 	entry = trace_event_buffer_reserve(&fbuffer, file, len);
 	if (entry) {
 		memcpy(entry, rec, len);