selftests/mm: gup_longterm: fix a resource leak

The opened file should be closed in run_with_tmpfile(), otherwise resource
leak will occur

Link: https://lkml.kernel.org/r/20230831093144.7520-1-dingxiang@cmss.chinamobile.comSigned-off-by: Ding Xiang <dingxiang@cmss.chinamobile.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/gup_longterm.c

@@ -265,10 +265,11 @@ static void run_with_tmpfile(test_fn fn, const char *desc)
 	fd = fileno(file);
 	if (fd < 0) {
 		ksft_test_result_fail("fileno() failed\n");
-		return;
+		goto close;
 	}
 
 	fn(fd, pagesize);
+close:
 	fclose(file);
 }