tracing: Make two symbols static

Fix sparse warnings:

kernel/trace/trace.c:6927:24: warning:
 symbol 'get_tracing_log_err' was not declared. Should it be static?
kernel/trace/trace.c:8196:15: warning:
 symbol 'trace_instance_dir' was not declared. Should it be static?

Link: http://lkml.kernel.org/r/20190614153210.24424-1-yuehaibing@huawei.comAcked-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -6923,7 +6923,7 @@ struct tracing_log_err {
 
 static DEFINE_MUTEX(tracing_err_log_lock);
 
-struct tracing_log_err *get_tracing_log_err(struct trace_array *tr)
+static struct tracing_log_err *get_tracing_log_err(struct trace_array *tr)
 {
 	struct tracing_log_err *err;
 
@@ -8192,7 +8192,7 @@ static const struct file_operations buffer_percent_fops = {
 	.llseek		= default_llseek,
 };
 
-struct dentry *trace_instance_dir;
+static struct dentry *trace_instance_dir;
 
 static void
 init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer);