tracing: Use __this_cpu_read() in trace_buffered_event_enable()

The code is executed with preemption disabled, so it's
safe to use __this_cpu_read().

Link: https://lkml.kernel.org/r/20200813112803.12256-1-tian.xianting@h3c.comSigned-off-by: Xianting Tian <tian.xianting@h3c.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -2511,7 +2511,7 @@ void trace_buffered_event_enable(void)
 
 		preempt_disable();
 		if (cpu == smp_processor_id() &&
-		    this_cpu_read(trace_buffered_event) !=
+		    __this_cpu_read(trace_buffered_event) !=
 		    per_cpu(trace_buffered_event, cpu))
 			WARN_ON_ONCE(1);
 		preempt_enable();