net/handshake: Fix handshake_dup() ref counting

If get_unused_fd_flags() fails, we ended up calling fput(sock->file)
twice.

Reported-by: Dan Carpenter <[e-mail]>
Suggested-by: Paolo Abeni <[e-mail]>
Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests")
Signed-off-by: Chuck Lever <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

net/handshake/netlink.c

···
 		goto out_complete;
 	}
 	err = req->hr_proto->hp_accept(req, info, fd);
-	if (err)
+	if (err) {
+		fput(sock->file);
 		goto out_complete;
+	}
 
 	trace_handshake_cmd_accept(net, req, req->hr_sk, fd);
 	return 0;
 
 out_complete:
 	handshake_complete(req, -EIO, NULL);
-	fput(sock->file);
 out_status:
 	trace_handshake_cmd_accept_err(net, req, NULL, err);
 	return err;