ALSA: compress: Use kzalloc() for ioctls writing back data

Like the previous patch by Dan, we should clear the data to be
returned from certain compress ioctls, namely,
snd_compr_get_codec_caps() and snd_compr_get_params().
This time, we can simply replace kmalloc() with kzalloc().

Signed-off-by: Takashi Iwai <tiwai@suse.de>