SDK / exoplayer

This can fix the following warning caused by commit a7aa84a8:

Warning: com.google.android.exoplayer2.drm.UnsupportedDrmException.Reason:
The typedef annotation should have @Retention(RetentionPolicy.SOURCE)

 Author:    Tony Guo <tony.guo.peng@gmail.com>
 Date:      Mon Feb 28 10:56:52 2022 +0800