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=94736


Reported-by: Daniela Doras-prodan <daniela.doras-prodan@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>