dm: sysfs add empty release function to avoid debug warning

This patch just removes an unnecessary warning:
 kobject: 'dm': does not have a release() function,
 it is broken and must be fixed.

The kobject is embedded in mapped device struct, so
code does not need to release memory explicitly here.

Cc: stable@kernel.org
Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-sysfs.c

@@ -79,13 +79,21 @@ static struct sysfs_ops dm_sysfs_ops = {
 	.show	= dm_attr_show,
 };
 
+/*
+ * The sysfs structure is embedded in md struct, nothing to do here
+ */
+static void dm_sysfs_release(struct kobject *kobj)
+{
+}
+
 /*
  * dm kobject is embedded in mapped_device structure
  * no need to define release function here
  */
 static struct kobj_type dm_ktype = {
 	.sysfs_ops	= &dm_sysfs_ops,
 	.default_attrs	= dm_attrs,
+	.release	= dm_sysfs_release
 };
 
 /*