ALSA: fireworks: Remove meaningless mutex_destroy()

Currently mutex_destroy() is called in module's cleanup function. But after
cleaned up, this mutex is automatically released. So this function call
is meaningless.

[fixed a typo in changelog by tiwai]
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/fireworks/fireworks.c

@@ -346,7 +346,6 @@ static void __exit snd_efw_exit(void)
 {
 	snd_efw_transaction_unregister();
 	driver_unregister(&efw_driver.driver);
-	mutex_destroy(&devices_mutex);
 }
 
 module_init(snd_efw_init);