fuse: fix root dentry initialization

Add missing dentry initialization to root dentry.

Fixes: f75fdf22b0a8 ("fuse: don't use ->d_time")
Reported-by: Andreas Reis <andreas.reis@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 1714109..6fe6a88 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1131,10 +1131,11 @@
 
 	err = -ENOMEM;
 	root = fuse_get_root_inode(sb, d.rootmode);
+	sb->s_d_op = &fuse_root_dentry_operations;
 	root_dentry = d_make_root(root);
 	if (!root_dentry)
 		goto err_dev_free;
-	/* only now - we want root dentry with NULL ->d_op */
+	/* Root dentry doesn't have .d_revalidate */
 	sb->s_d_op = &fuse_dentry_operations;
 
 	init_req = fuse_request_alloc(0);