gfs2: Don't return NULL from gfs2_inode_lookup

Callers expect gfs2_inode_lookup to return an inode pointer or ERR_PTR(error).
Commit b66648ad caused it to return NULL instead of ERR_PTR(-ESTALE) in
some cases.  Fix that.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: b66648ad ("gfs2: Move inode generation number check into gfs2_inode_lookup")
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/inode.c

@@ -207,10 +207,11 @@ struct inode *gfs2_inode_lookup(struct super_block *sb, unsigned int type,
 
 	if (no_formal_ino && ip->i_no_formal_ino &&
 	    no_formal_ino != ip->i_no_formal_ino) {
+		error = -ESTALE;
 		if (inode->i_state & I_NEW)
 			goto fail;
 		iput(inode);
-		return ERR_PTR(-ESTALE);
+		return ERR_PTR(error);
 	}
 
 	if (inode->i_state & I_NEW)