ALSA: cmi8328: Fix compile warnings without CONFIG_PM

Just add an ifdef CONFIG_PM to shut up the warnings:

  sound/isa/cmi8328.c:129:13: warning: ‘snd_cmi8328_cfg_save’ defined but not used [-Wunused-function]
  sound/isa/cmi8328.c:136:13: warning: ‘snd_cmi8328_cfg_restore’ defined but not used [-Wunused-function]

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