[ALSA] at73c213: remove redundant private_free routine

snd_pcm_lib_preallocate_free_for_all() is called from snd_pcm_free() just
after calling the private_free routine.  So there should be no need to call
it in driver's private_free routine.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>