btrfs: cleanup find_device() drop list_head pointer

find_device() declares struct list_head *head pointer and used only once,
instead just use it directly.
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -362,10 +362,9 @@ static struct btrfs_device *__alloc_device(void)
 static struct btrfs_device *find_device(struct btrfs_fs_devices *fs_devices,
 		u64 devid, const u8 *uuid)
 {
-	struct list_head *head = &fs_devices->devices;
 	struct btrfs_device *dev;
 
-	list_for_each_entry(dev, head, dev_list) {
+	list_for_each_entry(dev, &fs_devices->devices, dev_list) {
 		if (dev->devid == devid &&
 		    (!uuid || !memcmp(dev->uuid, uuid, BTRFS_UUID_SIZE))) {
 			return dev;