use C99 initializers for audio_pcm_ops

Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/audio/wavaudio.c b/audio/wavaudio.c
index 51ed6eb..4c49f23 100644
--- a/audio/wavaudio.c
+++ b/audio/wavaudio.c
@@ -239,17 +239,11 @@
 };
 
 static struct audio_pcm_ops wav_pcm_ops = {
-    wav_init_out,
-    wav_fini_out,
-    wav_run_out,
-    wav_write_out,
-    wav_ctl_out,
-
-    NULL,
-    NULL,
-    NULL,
-    NULL,
-    NULL
+    .init_out = wav_init_out,
+    .fini_out = wav_fini_out,
+    .run_out  = wav_run_out,
+    .write    = wav_write_out,
+    .ctl_out  = wav_ctl_out,
 };
 
 struct audio_driver wav_audio_driver = {