firewire: core: fix possible memory leak in create_units()

If device_register() fails, the refcount of device is not 0, the name
allocated in dev_set_name() is leaked. To fix this by calling put_device(),
so that it will be freed in callback function kobject_cleanup().

unreferenced object 0xffff9d99035c7a90 (size 8):
  comm "systemd-udevd", pid 168, jiffies 4294672386 (age 152.089s)
  hex dump (first 8 bytes):
    66 77 30 2e 30 00 ff ff                          fw0.0...
  backtrace:
    [<00000000e1d62bac>] __kmem_cache_alloc_node+0x1e9/0x360
    [<00000000bbeaff31>] __kmalloc_node_track_caller+0x44/0x1a0
    [<00000000491f2fb4>] kvasprintf+0x67/0xd0
    [<000000005b960ddc>] kobject_set_name_vargs+0x1e/0x90
    [<00000000427ac591>] dev_set_name+0x4e/0x70
    [<000000003b4e447d>] create_units+0xc5/0x110

fw_unit_release() will be called in the error path, move fw_device_get()
before calling device_register() to keep balanced with fw_device_put() in
fw_unit_release().

Cc: stable@vger.kernel.org
Fixes: 1fa5ae85 ("driver core: get rid of struct device's bus_id string array")
Fixes: a1f64819 ("firewire: struct device - replace bus_id with dev_name(), dev_set_name()")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

drivers/firewire/core-device.c

@@ -717,14 +717,11 @@ static void create_units(struct fw_device *device)
 					fw_unit_attributes,
 					&unit->attribute_group);
 
-		if (device_register(&unit->device) < 0)
-			goto skip_unit;
-
 		fw_device_get(device);
-		continue;
-
-	skip_unit:
-		kfree(unit);
+		if (device_register(&unit->device) < 0) {
+			put_device(&unit->device);
+			continue;
+		}
 	}
 }