ALSA: fireface: code refactoring to parse of clock configuration

A procedure to retrieve clock configuration is used by two callers.
Each of caller has duplicated code to parse bits.

This commit adds refactoring to remove the duplicated code.

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