Partition, ...: use libfmt for logging

src/mixer/Volume.cxx

@@ -106,8 +106,8 @@ read_sw_volume_state(const char *line, MultipleOutputs &outputs)
 	if (*end == 0 && sv >= 0 && sv <= 100)
 		software_volume_change(outputs, sv);
 	else
-		FormatWarning(volume_domain,
-			      "Can't parse software volume: %s", line);
+		FmtWarning(volume_domain,
+			   "Can't parse software volume: {}", line);
 	return true;
 }
 

src/mixer/plugins/AlsaMixerPlugin.cxx

@@ -125,9 +125,9 @@ AlsaMixerMonitor::DispatchSockets() noexcept
 
 	int err = snd_mixer_handle_events(mixer);
 	if (err < 0) {
-		FormatError(alsa_mixer_domain,
-			    "snd_mixer_handle_events() failed: %s",
-			    snd_strerror(err));
+		FmtError(alsa_mixer_domain,
+			 "snd_mixer_handle_events() failed: {}",
+			 snd_strerror(err));
 
 		if (err == -ENODEV) {
 			/* the sound device was unplugged; disable