ALSA: hda - Clear the leftover component assignment at snd_hdac_i915_exit()

The commit [d745f5e7: ALSA: hda - Add the pin / port mapping on
Intel ILK and VLV] introduced a WARN_ON() to check the pointer for
avoiding the double initializations.  But hdac_acomp pointer wasn't
cleared at snd_hdac_i915_exit(), thus after reloading the HD-audio
driver, it may result in the false positive warning.  This patch makes
sure to clear the leftover pointer at exit.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94736Reported-by: Daniela Doras-prodan <daniela.doras-prodan@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/hda/hdac_i915.c

@@ -372,6 +372,7 @@ int snd_hdac_i915_exit(struct hdac_bus *bus)
 
 	kfree(acomp);
 	bus->audio_component = NULL;
+	hdac_acomp = NULL;
 
 	return 0;
 }