NFSv4: Ensure nfs_atomic_open set the dentry verifier on ENOENT

If the OPEN rpc call to the server fails with an ENOENT call, nfs_atomic_open
will create a negative dentry for that file, however it currently fails
to call nfs_set_verifier(), thus causing the dentry to be immediately
revalidated on the next call to nfs_lookup_revalidate() instead of following
the usual lookup caching rules.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/dir.c

@@ -1527,6 +1527,7 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
 		case -ENOENT:
 			d_drop(dentry);
 			d_add(dentry, NULL);
+			nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
 			break;
 		case -EISDIR:
 		case -ENOTDIR: