ALSA: memalloc: NULL-initialize in snd_malloc_dev_iram()

dmab->area and addr fields should be cleared at the head of
snd_malloc_dev_iram() as especially dmab->area is used to indicate the
allocation failure / fallback.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/memalloc.c

@@ -172,6 +172,9 @@ static void snd_malloc_dev_iram(struct snd_dma_buffer *dmab, size_t size)
 	struct device *dev = dmab->dev.dev;
 	struct gen_pool *pool = NULL;
 
+	dmab->area = NULL;
+	dmab->addr = 0;
+
 	if (dev->of_node)
 		pool = of_get_named_gen_pool(dev->of_node, "iram", 0);