ALSA: firewire-lib: Remove a comment about restriction of asynchronous operation

The comment for fcp_avc_transaction() describes it doesn't support this type
of operation. But it was already supported by this commit.

00a7bb81c20f3e81711e28e0f6c08cee8fd18514
ALSA: firewire-lib: Add support for deferred transaction

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

sound/firewire/fcp.c

@@ -218,8 +218,6 @@ struct fcp_transaction {
  *
  * @command and @response can point to the same buffer.
  *
- * Asynchronous operation (INTERIM, NOTIFY) is not supported at the moment.
- *
  * Returns the actual size of the response frame, or a negative error code.
  */
 int fcp_avc_transaction(struct fw_unit *unit,