block/rnbd-clt-sysfs: use default_groups in kobj_type

There are currently 2 ways to create a set of sysfs files for a
kobj_type, through the default_attrs field, and the default_groups
field.  Move the rnbd controller sysfs code to use default_groups field
which has been the preferred way since aa30f47c ("kobject: Add
support for default attribute groups to kobj_type") so that we can soon
get rid of the obsolete default_attrs field.

Cc: "Md. Haris Iqbal" <haris.iqbal@ionos.com>
Cc: Jack Wang <jinpu.wang@ionos.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Jack Wang <jinpu.wang@ionos.com>
Link: https://lore.kernel.org/r/20220104162947.1320936-1-gregkh@linuxfoundation.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/rnbd/rnbd-clt-sysfs.c

@@ -452,6 +452,7 @@ static struct attribute *rnbd_dev_attrs[] = {
 	&rnbd_clt_nr_poll_queues.attr,
 	NULL,
 };
+ATTRIBUTE_GROUPS(rnbd_dev);
 
 void rnbd_clt_remove_dev_symlink(struct rnbd_clt_dev *dev)
 {
@@ -474,7 +475,7 @@ void rnbd_clt_remove_dev_symlink(struct rnbd_clt_dev *dev)
 
 static struct kobj_type rnbd_dev_ktype = {
 	.sysfs_ops      = &kobj_sysfs_ops,
-	.default_attrs  = rnbd_dev_attrs,
+	.default_groups = rnbd_dev_groups,
 };
 
 static int rnbd_clt_add_dev_kobj(struct rnbd_clt_dev *dev)