Fix a warning in libvpxJNI
Fix a warning in libvpxJNI

v2/extensions/vp9/src/main/jni/vpx_jni.cc:63:31: warning: missing field 'w' initializer [-Wmissing-field-initializers]
  vpx_codec_dec_cfg_t cfg = {0};
                              ^

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=132461351

reid-mcpherson/ExoPlayerDebug,reid-mcpherson/ExoPlayerDebug,Dysonics/ExoPlayer,reid-mcpherson/ExoPlayerDebug,Dysonics/ExoPlayer,Dysonics/ExoPlayer