ALSA: firewire-tascam: use the same address for asynchronous transaction for MIDI message

Units on TASCAM FireWire series receive MIDI messages by asynchronous
transactions on IEEE 1394 bus. Although the transaction is sent to a
certain register, current ALSA driver for this series has a redundant design.

This commit use the same address for the transaction.

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