Fix javadocs typos

Issue:#2773

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=155062917

extensions/vp9/src/main/java/com/google/android/exoplayer2/ext/vp9/LibvpxVideoRenderer.java

@@ -286,7 +286,7 @@ public final class LibvpxVideoRenderer extends BaseRenderer {
    *
    * @param outputBufferTimeUs The timestamp of the current output buffer.
    * @param nextOutputBufferTimeUs The timestamp of the next output buffer or
-   *     {@link TIME_UNSET} if the next output buffer is unavailable.
+   *     {@link C#TIME_UNSET} if the next output buffer is unavailable.
    * @param positionUs The current playback position.
    * @param joiningDeadlineMs The joining deadline.
    * @return Returns whether to drop the current output buffer.

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheUtil.java

@@ -64,7 +64,7 @@ public final class CacheUtil {
   }
 
   /**
-   * Returns already cached and missing bytes in the {@cache} for the data defined by {@code
+   * Returns already cached and missing bytes in the {@code cache} for the data defined by {@code
    * dataSpec}.
    *
    * @param dataSpec Defines the data to be checked.