vfs: prefer ->dentry->d_sb to ->mnt->mnt_sb

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/nfsd/nfsctl.c

@@ -272,7 +272,7 @@ static ssize_t write_unlock_fs(struct file *file, char *buf, size_t size)
 	 * 2.  Is that directory a mount point, or
 	 * 3.  Is that directory the root of an exported file system?
 	 */
-	error = nlmsvc_unlock_all_by_sb(path.mnt->mnt_sb);
+	error = nlmsvc_unlock_all_by_sb(path.dentry->d_sb);
 
 	path_put(&path);
 	return error;