ALSA: pcm: add a helper function to constrain interval-type parameters

Application of constraints to interval-type parameters for PCM substream
is done in a call of snd_pcm_hw_refine(), while the function includes
much codes and is not enough friendly to readers.

This commit splits the codes to a separated function so that readers can
get it easily. I leave desicion into compilers to merge the function into
its callee.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>