ALSA: hda/sigmatel: Fix unused variable warning for beep power change

The newly added stac_check_power_status() caused a compile warning
when CONFIG_SND_HDA_INPUT_BEEP is disabled.  Fix it.

Fixes: 414d38ba ("ALSA: hda/sigmatel: Keep power up while beep is enabled")
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20220905130630.2845-1-tiwai@suse.de


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