ALSA: hda - Fix unused label skip_i915

When CONFIG_SND_HDA_I915=n, we get a compile warning:
  sound/pci/hda/hda_intel.c: In function ‘azx_probe_continue’:
  sound/pci/hda/hda_intel.c:1882:2: warning: label ‘skip_i915’ defined but not used [-Wunused-label]

Fix it by putting again ifdef to it.  Sigh.

Fixes: bf06848b ('ALSA: hda - Continue probing even if i915 binding fails')
Reported-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>