Disambiguate comment in Ac3Reader

PiperOrigin-RevId: 239810798

library/core/src/main/java/com/google/android/exoplayer2/extractor/ts/Ac3Reader.java

@@ -201,7 +201,7 @@ public final class Ac3Reader implements ElementaryStreamReader {
       output.format(format);
     }
     sampleSize = frameInfo.frameSize;
-    // In this class a sample is an access unit (syncframe in AC-3), but the MediaFormat sample rate
+    // In this class a sample is an access unit (syncframe in AC-3), but Format#sampleRate
     // specifies the number of PCM audio samples per second.
     sampleDurationUs = C.MICROS_PER_SECOND * frameInfo.sampleCount / format.sampleRate;
   }