nfsd: open-code special directory-hardlink check

We allow the fh_verify caller to specify that any object *except* those
of a given type is allowed, by passing a negative type.  But only one
caller actually uses it.  Open-code that check in the one caller.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index fd0acca..0c92a17 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1632,10 +1632,12 @@
 	err = fh_verify(rqstp, ffhp, S_IFDIR, NFSD_MAY_CREATE);
 	if (err)
 		goto out;
-	err = fh_verify(rqstp, tfhp, -S_IFDIR, NFSD_MAY_NOP);
+	err = fh_verify(rqstp, tfhp, 0, NFSD_MAY_NOP);
 	if (err)
 		goto out;
-
+	err = nfserr_isdir;
+	if (S_ISDIR(tfhp->fh_dentry->d_inode->i_mode))
+		goto out;
 	err = nfserr_perm;
 	if (!len)
 		goto out;