btrfs: kill magical embedded struct superblock

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index cb170ca..ecf0fac 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6900,7 +6900,7 @@
 {
 	struct inode *inode = dentry->d_inode;
 	generic_fillattr(inode, stat);
-	stat->dev = BTRFS_I(inode)->root->anon_super.s_dev;
+	stat->dev = BTRFS_I(inode)->root->anon_dev;
 	stat->blksize = PAGE_CACHE_SIZE;
 	stat->blocks = (inode_get_bytes(inode) +
 			BTRFS_I(inode)->delalloc_bytes) >> 9;