uml: helper.c warning corrections

Fix this warning:

  arch/um/os-Linux/helper.c: In function `helper_child':
  arch/um/os-Linux/helper.c:38:7: warning: ignoring return value of `write', declared with attribute warn_unused_result

[richard@nod.at: happens only with -D_FORTIFY_SOURCE=2]
Signed-off-by: Vitaliy Ivanov <vitalivanov@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/os-Linux/helper.c

@@ -28,14 +28,14 @@ static int helper_child(void *arg)
 {
 	struct helper_data *data = arg;
 	char **argv = data->argv;
-	int err;
+	int err, ret;
 
 	if (data->pre_exec != NULL)
 		(*data->pre_exec)(data->pre_data);
 	err = execvp_noalloc(data->buf, argv[0], argv);
 
 	/* If the exec succeeds, we don't get here */
-	write(data->fd, &err, sizeof(err));
+	CATCH_EINTR(ret = write(data->fd, &err, sizeof(err)));
 
 	return 0;
 }