ALSA: hdspm - Drop duplicate code in hdspm_set_system_clock_mode()

hdspm_set_system_clock_mode() is almost a one-by-one copy of
hdspm_set_toggle_setting(). To improve code quality, remove the
duplication.

Signed-off-by: Adrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>