audio: return Error ** from audio_state_by_name

Remove duplicate error formatting code.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/audio/audio.c b/audio/audio.c
index fdc34a7..874a4c3 100644
--- a/audio/audio.c
+++ b/audio/audio.c
@@ -2260,7 +2260,7 @@
         audioformat_bytes_per_sample(as->fmt);
 }
 
-AudioState *audio_state_by_name(const char *name)
+AudioState *audio_state_by_name(const char *name, Error **errp)
 {
     AudioState *s;
     QTAILQ_FOREACH(s, &audio_states, list) {
@@ -2269,6 +2269,7 @@
             return s;
         }
     }
+    error_setg(errp, "audiodev '%s' not found", name);
     return NULL;
 }