[ALSA] ac97_patch: compilation warning fix

This patch kills these two compilation warnings if
power management is disabled:
sound/pci/ac97/ac97_patch.h:86: warning: 'snd_ac97_restore_status'
declared 'static' but never defined
sound/pci/ac97/ac97_patch.h:87: warning: 'snd_ac97_restore_iec958'
declared 'static' but never defined

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>