ALSA: oxygen: Remove unnecessary snd_pcm_lib_preallocate_free_for_all()

The ALSA core takes care that all preallocated memory is freed when the PCM
itself is freed. There is no need to do this manually in the driver.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>