um: return negative in tuntap_open_tramp()

The intention is to return negative error codes.  "pid" is already
negative but we accidentally negate it again back to positive.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/os-Linux/drivers/tuntap_user.c

@@ -80,7 +80,7 @@ static int tuntap_open_tramp(char *gate, int *fd_out, int me, int remote,
 	pid = run_helper(tuntap_pre_exec, &data, argv);
 
 	if (pid < 0)
-		return -pid;
+		return pid;
 
 	close(remote);