ALSA: firewire-lib: add a restriction for a transaction at once

Currently, when waiting for a response, callers can start another
transaction by scheduling another work. This is not good for error
processing of transaction, especially the first response is too late.

This commit serialize request/response transactions, by adding one
boolean member to represent idling state.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/lib.h

@@ -30,6 +30,7 @@ typedef int (*snd_fw_async_midi_port_fill)(
 struct snd_fw_async_midi_port {
 	struct fw_device *parent;
 	struct work_struct work;
+	bool idling;
 
 	u64 addr;
 	struct fw_transaction transaction;