Fix up the first rawmidi port alias.

This lacked a proper device prefix and thus wouldn't show in qjackctl,
so that the Jack MIDI connections view came up empty. Added the system:
prefix so that they will now be displayed correctly.

linux/alsa/alsa_rawmidi.c

@@ -500,11 +500,11 @@ int midi_port_open(alsa_rawmidi_t *midi, midi_port_t *port)
 
 	/* Some devices (emu10k1) have subdevs with the same name,
 	 * and we need to generate unique port name for jack */
-	strncpy(name, port->name, sizeof(name));
+	snprintf(name, sizeof(name), "system:%s", port->name);
 	if (midi_port_open_jack(midi, port, type, name)) {
 		int num;
 		num = port->id.id[3] ? port->id.id[3] : port->id.id[1];
-		snprintf(name, sizeof(name), "%s %d", port->name, num);
+		snprintf(name, sizeof(name), "system:%s %d", port->name, num);
 		if (midi_port_open_jack(midi, port, type, name))
 			return 2;
 	}