ALSA: hda: tegra: Fix unused variable compile warning

ALSA: hda: tegra: Fix unused variable compile warning

Forgot to remove the variable declaration as well in the last commit.
  sound/pci/hda/hda_tegra.c: In function 'hda_tegra_runtime_suspend':
  sound/pci/hda/hda_tegra.c:169:19: warning: unused variable 'bus' [-Wunused-variable]

Fixes: 967ea8917910 ("ALSA: hda: Support PCM sync_stop")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/r/20191212080518.6522-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>