mvp: fall back to 16 bit audio samples

Looks like the MVP audio output only supports 16 and 24 bit audio
samples.  If MPD generates any other sample formats, force it to use
16 bit.

src/output/mvp_plugin.c

@@ -152,7 +152,11 @@ mvp_set_pcm_params(struct mvp_data *md, struct audio_format *audio_format)
 		break;
 
 	default:
-		return false;
+		g_debug("unsupported sample format %u - falling back to stereo",
+			audio_format->bits);
+		audio_format->bits = 16;
+		mix[1] = 2;
+		break;
 	}
 
 	mix[3] = 0;	/* stream type? */