ALSA: hda: Fix build warning

The hda_tegra_disable_clocks() function is only used by the suspend and
resume code, so it needs to be included in the #ifdef CONFIG_PM_SLEEP
block to prevent the following warning:

  CC      sound/pci/hda/hda_tegra.o
sound/pci/hda/hda_tegra.c:238:13: warning: 'hda_tegra_disable_clocks' defined but not used [-Wunused-function]
 static void hda_tegra_disable_clocks(struct hda_tegra *data)
             ^

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>