[ALSA] ac97 - NULL check in snd_ac97_suspend/resume

Modules: AC97 Codec

Add NULL check in snd_ac97_suspend() and snd_ac97_resume() so that
the caller doesn't have to do it by itself.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/ac97/ac97_codec.c

@@ -2186,6 +2186,8 @@ static void snd_ac97_powerdown(struct snd_ac97 *ac97)
  */
 void snd_ac97_suspend(struct snd_ac97 *ac97)
 {
+	if (! ac97)
+		return;
 	if (ac97->build_ops->suspend)
 		ac97->build_ops->suspend(ac97);
 	snd_ac97_powerdown(ac97);
@@ -2242,6 +2244,9 @@ void snd_ac97_resume(struct snd_ac97 *ac97)
 {
 	unsigned long end_time;
 
+	if (! ac97)
+		return;
+
 	if (ac97->bus->ops->reset) {
 		ac97->bus->ops->reset(ac97);
 		goto  __reset_ready;