At present, to check running stream, available stream formats are used
at current sampling transmission frequency (stf). But when changing stf,
it's convenient to use cache of stream formats.

This commit applies this idea.
Signed-off-by: NTakashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>