ALSA: sound: Move dereference after NULL test and drop unnecessary NULL tests

In pcm.c, if the NULL test on pcm is needed, then the dereference should be
after the NULL test.

In dummy.c and ali5451.c, the context of the calls to
snd_card_dummy_new_mixer and snd_ali_free_voice show that dummy and pvoice,
respectively cannot be NULL.

A simplified version of the semantic match that detects this problem is as
follows (http://coccinelle.lip6.fr/):

// <smpl>
@match exists@
expression x, E;
identifier fld;
@@

* x->fld
  ... when != \(x = E\|&x\)
* x == NULL
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm.c

@@ -953,11 +953,12 @@ static int snd_pcm_dev_register(struct snd_device *device)
 	struct snd_pcm_substream *substream;
 	struct snd_pcm_notify *notify;
 	char str[16];
-	struct snd_pcm *pcm = device->device_data;
+	struct snd_pcm *pcm;
 	struct device *dev;
 
-	if (snd_BUG_ON(!pcm || !device))
+	if (snd_BUG_ON(!device || !device->device_data))
 		return -ENXIO;
+	pcm = device->device_data;
 	mutex_lock(&register_mutex);
 	err = snd_pcm_add(pcm);
 	if (err) {

sound/drivers/dummy.c

@@ -808,8 +808,6 @@ static int __devinit snd_card_dummy_new_mixer(struct snd_dummy *dummy)
 	unsigned int idx;
 	int err;
 
-	if (snd_BUG_ON(!dummy))
-		return -EINVAL;
 	spin_lock_init(&dummy->mixer_lock);
 	strcpy(card->mixername, "Dummy Mixer");
 

sound/pci/ali5451/ali5451.c

@@ -973,7 +973,7 @@ static void snd_ali_free_voice(struct snd_ali * codec,
 	void *private_data;
 
 	snd_ali_printk("free_voice: channel=%d\n",pvoice->number);
-	if (pvoice == NULL || !pvoice->use)
+	if (!pvoice->use)
 		return;
 	snd_ali_clear_voices(codec, pvoice->number, pvoice->number);
 	spin_lock_irq(&codec->voice_alloc);