tests: use vpx_codec_dec_cfg_t() to initialize vars

0-initializes [1] and removes a warning for missing initializer fields

[1] http://en.cppreference.com/w/cpp/language/value_initialization

Change-Id: I364248010c8fa663c71d8f06a9999c730e92db4c
diff --git a/test/svc_test.cc b/test/svc_test.cc
index 1cb01a4..23e727a 100644
--- a/test/svc_test.cc
+++ b/test/svc_test.cc
@@ -60,7 +60,7 @@
     codec_enc_.kf_min_dist = 100;
     codec_enc_.kf_max_dist = 100;
 
-    vpx_codec_dec_cfg_t dec_cfg = {0};
+    vpx_codec_dec_cfg_t dec_cfg = vpx_codec_dec_cfg_t();
     VP9CodecFactory codec_factory;
     decoder_ = codec_factory.CreateDecoder(dec_cfg, 0);
   }