ALSA: hda - Don't call vmaster hook when bus->shutdown is set

The flag bus->shutdown implies that the control elements might have
been already destroyed.  When a codec is resumed at this state and
tries to call vmaster hook (e.g. in snd_hda_gen_init()), it would
refer to a non-existing object, resulting in Oops in the end.

This patch just adds a check of the flag in the caller side for
avoiding such a crash.

Though, the best would be to clear hook->sw_kctl by the destructor of
the corresponding ctl element, but vmaster uses its own private_free,
it can't be done easily.  So let it be for a while.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/hda_codec.c

@@ -2784,6 +2784,11 @@ void snd_hda_sync_vmaster_hook(struct hda_vmaster_mute_hook *hook)
 {
 	if (!hook->hook || !hook->codec)
 		return;
+	/* don't call vmaster hook in the destructor since it might have
+	 * been already destroyed
+	 */
+	if (hook->codec->bus->shutdown)
+		return;
 	switch (hook->mute_mode) {
 	case HDA_VMUTE_FOLLOW_MASTER:
 		snd_ctl_sync_vmaster_hook(hook->sw_kctl);