9p: potential ERR_PTR() dereference

p9_client_walk() can return error values if we run out of space or there
is a problem with the network.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

fs/9p/fid.c

@@ -242,6 +242,7 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
 	}
 	kfree(wnames);
 fid_out:
+	if (!IS_ERR(fid))
 		v9fs_fid_add(dentry, fid);
 err_out:
 	up_read(&v9ses->rename_sem);