ALSA: firewire: Use managed buffer allocation

Clean up the drivers with the new managed buffer allocation API.
The superfluous snd_pcm_lib_malloc_pages() and
snd_pcm_lib_free_pages() calls are dropped.

Acked-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20191209192422.23902-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>