NFS: Don't hard-code the fs_type when submounting

Hard-coding the fstype causes "nfs4" mounts to appear as "nfs",
which breaks scripts that do "umount -at nfs4".
Reported-by: Patrick Steinhardt <ps@pks.im>
Fixes: f2aedb71 ("NFS: Add fs_context support.")
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/namespace.c

@@ -153,7 +153,7 @@ struct vfsmount *nfs_d_automount(struct path *path)
 	/* Open a new filesystem context, transferring parameters from the
 	 * parent superblock, including the network namespace.
 	 */
-	fc = fs_context_for_submount(&nfs_fs_type, path->dentry);
+	fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, path->dentry);
 	if (IS_ERR(fc))
 		return ERR_CAST(fc);