ALSA: hda - Fix warnings with CONFIG_SND_POWER_SAVE=n

Use static inline for dummy function to fix the warnings like below
  sound/pci/hda/patch_sigmatel.c: In function ‘stac92xx_init’:
  sound/pci/hda/patch_sigmatel.c:4387:3: warning: statement with no effect
  sound/pci/hda/patch_sigmatel.c: In function ‘stac92xx_resume’:
  sound/pci/hda/patch_sigmatel.c:4927:3: warning: statement with no effect

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