RDMA/core: Use simpler device_del() instead of device_unregister()

Instead of holding extra reference using get_device() that
device_unregister() releases, simplify it as below.

device_add() balances with device_del().  device_initialize() balances
with put_device(), always via ib_dealloc_device().

Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/device.c

@@ -369,6 +369,7 @@ void ib_dealloc_device(struct ib_device *device)
 	WARN_ON(!xa_empty(&device->client_data));
 	WARN_ON(refcount_read(&device->refcount));
 	rdma_restrack_clean(device);
+	/* Balances with device_initialize */
 	put_device(&device->dev);
 }
 EXPORT_SYMBOL(ib_dealloc_device);

drivers/infiniband/core/sysfs.c

@@ -1351,15 +1351,12 @@ int ib_device_register_sysfs(struct ib_device *device)
 
 void ib_device_unregister_sysfs(struct ib_device *device)
 {
-	/* Hold device until ib_dealloc_device() */
-	get_device(&device->dev);
-
 	free_port_list_attributes(device);
 
 	if (device->hw_stats) {
 		kfree(device->hw_stats);
 		free_hsag(&device->dev.kobj, device->hw_stats_ag);
 	}
-
-	device_unregister(&device->dev);
+	/* Balances with device_add */
+	device_del(&device->dev);
 }