ALSA: hda - Fix unused variable warning

The unused variable was forgotten to be removed and now we get a
compiler warning:
  sound/pci/hda/hda_codec.c: In function 'hda_codec_runtime_suspend':
  sound/pci/hda/hda_codec.c:2926:18: warning: unused variable 'pcm'

Fixes: 17bc4815 ("ALSA: pci: Remove superfluous snd_pcm_suspend*() calls")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Takashi Iwai <tiwai@suse.de>