media: correctly return cached size for MediaDataSource

Bug: 27431229
Change-Id: I884e43960789c139b48964deba8f56b3bc3ba590
diff --git a/media/jni/android_media_MediaDataSource.cpp b/media/jni/android_media_MediaDataSource.cpp
index 025133f..ecd10c7 100644
--- a/media/jni/android_media_MediaDataSource.cpp
+++ b/media/jni/android_media_MediaDataSource.cpp
@@ -116,7 +116,8 @@
         return UNKNOWN_ERROR;
     }
     if (mSizeIsCached) {
-        return mCachedSize;
+        *size = mCachedSize;
+        return OK;
     }
 
     JNIEnv* env = AndroidRuntime::getJNIEnv();