ALSA: fireworks: code refactoring for rawmidi.open/close

Two sets of callbacks for rawmidi.open/close but they have the same
codes. This commit unifies each of the callbacks.

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