[ALSA] Add error messages

Add error messages in the critial error path to be more verbose.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/core/device.c b/sound/core/device.c
index afa8cc7..b1cf6ec 100644
--- a/sound/core/device.c
+++ b/sound/core/device.c
@@ -50,8 +50,10 @@
 	snd_assert(device_data != NULL, return -ENXIO);
 	snd_assert(ops != NULL, return -ENXIO);
 	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
-	if (dev == NULL)
+	if (dev == NULL) {
+		snd_printk(KERN_ERR "Cannot allocate device\n");
 		return -ENOMEM;
+	}
 	dev->card = card;
 	dev->type = type;
 	dev->state = SNDRV_DEV_BUILD;
@@ -173,6 +175,7 @@
 			dev->state = SNDRV_DEV_REGISTERED;
 			return 0;
 		}
+		snd_printd("snd_device_register busy\n");
 		return -EBUSY;
 	}
 	snd_BUG();