tracing: fix typos in comments

Impact: clean up.

Fix typos in the comments.

Signed-off-by: Wenji Huang <wenji.huang@oracle.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 3c103d6..8e6646a 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -8,7 +8,7 @@
 struct ring_buffer_iter;
 
 /*
- * Don't reference this struct directly, use functions below.
+ * Don't refer to this struct directly, use functions below.
  */
 struct ring_buffer_event {
 	u32		type:2, len:3, time_delta:27;