ALSA: Create sysfs attribute files via groups

Instead of calling each time device_create_file(), create the groups
of sysfs attribute files at once in a normal way.  Add a new helper
function, snd_get_device(), to return the associated device object,
so that we can handle the sysfs addition locally.

Since the sysfs file addition is done differently now,
snd_add_device_sysfs_file() helper function is removed.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/include/sound/core.h b/include/sound/core.h
index a3e3e89..9c11873 100644
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -248,8 +248,7 @@
 
 int snd_unregister_device(int type, struct snd_card *card, int dev);
 void *snd_lookup_minor_data(unsigned int minor, int type);
-int snd_add_device_sysfs_file(int type, struct snd_card *card, int dev,
-			      struct device_attribute *attr);
+struct device *snd_get_device(int type, struct snd_card *card, int dev);
 
 #ifdef CONFIG_SND_OSSEMUL
 int snd_register_oss_device(int type, struct snd_card *card, int dev,