ALSA: snd-firewire-lib: remove unused header inclusion

spinlock is not used in amdtp.h.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/amdtp.h

@@ -3,7 +3,6 @@
 
 #include <linux/interrupt.h>
 #include <linux/mutex.h>
-#include <linux/spinlock.h>
 #include "packets-buffer.h"
 
 /**