CCodec: add more doc to PipelineWatcher

Test: builds
Change-Id: Id6534cd2b4f5c68ee568ada06a8c2bb73584c275
diff --git a/media/codec2/sfplugin/PipelineWatcher.cpp b/media/codec2/sfplugin/PipelineWatcher.cpp
index cdcc41b..df81d49 100644
--- a/media/codec2/sfplugin/PipelineWatcher.cpp
+++ b/media/codec2/sfplugin/PipelineWatcher.cpp
@@ -139,8 +139,8 @@
               std::chrono::duration_cast<std::chrono::milliseconds>(elapsed).count());
         durations.push_back(elapsed);
     }
-    nth_element(durations.begin(), durations.end(), durations.begin() + n,
-                std::greater<Clock::duration>());
+    std::nth_element(durations.begin(), durations.end(), durations.begin() + n,
+                     std::greater<Clock::duration>());
     return durations[n];
 }