ALSA: pcm: Make snd_pcm_hw_constraints_init() and _complete() static

Both snd_pcm_hw_constraints_init() and _complete() functions are
called only from pcm_native.c, hence they can be static for further
optimization.

Link: https://lore.kernel.org/r/20200116162825.24792-1-tiwai@suse.de


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