Fix an example in SequenceChecker documentation

SequenceChecker needs to be prefixed with & in RTC_DCHECK_RUN_ON;
all examples except the first one were showing this.

Bug: none
Change-Id: I90468689675319f9df67eb04a5d4cc0767ffb7a9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215582
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33771}
diff --git a/api/sequence_checker.h b/api/sequence_checker.h
index 6b46128..5db7b9e 100644
--- a/api/sequence_checker.h
+++ b/api/sequence_checker.h
@@ -26,7 +26,7 @@
 // class MyClass {
 //  public:
 //   void Foo() {
-//     RTC_DCHECK_RUN_ON(sequence_checker_);
+//     RTC_DCHECK_RUN_ON(&sequence_checker_);
 //     ... (do stuff) ...
 //   }
 //