btrfs: move btrfs_rm_dev_replace_free_srcdev outside of all locks

When closing and freeing the source device we could end up doing our
final blkdev_put() on the bdev, which will grab the bd_mutex.  As such
we want to be holding as few locks as possible, so move this call
outside of the dev_replace->lock_finishing_cancel_unmount lock.  Since
we're modifying the fs_devices we need to make sure we're holding the
uuid_mutex here, so take that as well.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -2216,7 +2216,6 @@ void btrfs_rm_dev_replace_remove_srcdev(struct btrfs_device *srcdev)
 
 void btrfs_rm_dev_replace_free_srcdev(struct btrfs_device *srcdev)
 {
-	struct btrfs_fs_info *fs_info = srcdev->fs_info;
 	struct btrfs_fs_devices *fs_devices = srcdev->fs_devices;
 
 	mutex_lock(&uuid_mutex);