ALSA: hda: Skip event processing for unregistered codecs

When codec is unbound but not yet removed, in the eyes of
snd_hdac_bus_process_unsol_events() it is still a valid target to
delegate work to. Such behaviour may lead to use-after-free errors.
Address by verifying if codec is actually registered.

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20220706120230.427296-6-cezary.rojewski@intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>