Btrfs: trivial sparse fixes

Fix a bunch of trivial sparse complaints.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 59b64c7..f84b5f6 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -739,7 +739,7 @@
 		goto out;
 	}
 	btrfs_end_transaction(trans, root);
-	file->private_data = 0;
+	file->private_data = NULL;
 
 	mutex_lock(&root->fs_info->trans_mutex);
 	root->fs_info->open_ioctl_trans--;