A helper function used by snd_pcm_hw_refine() still keeps using VLA
for timestamps of hw constraint rules that are non-fixed size.
Let's replace the VLA with a simple kmalloc() array.
Reference: https://lkml.org/lkml/2018/3/7/621
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>