selftests/mm temporary fix of hmm infinite loop

jira SECO-170

In Rocky9 if you run ./run_vmtests.sh -t hmm it will fail and cause an
infinite loop on ASSERTs in FIXTURE_TEARDOWN()
This temporary fix is based on the discussion here
https://patchwork.kernel.org/project/linux-kselftest/patch/26017fe3-5ad7-6946-57db-e5ec48063ceb@suse.cz/#25046055

We will investigate further kselftest updates that will resolve the root
causes of this.

Signed-off-by: Jonathan Maple <jmaple@ciq.com>

Author: PlaidCat

tools/testing/selftests/mm/hmm-tests.c

@@ -159,6 +159,10 @@ FIXTURE_TEARDOWN(hmm)
 {
 	int ret = close(self->fd);
 
+	if (ret != 0) {
+		fprintf(stderr, "close returned (%d) fd is (%d)\n", ret, self->fd);
+		exit(1);
+	}
 	ASSERT_EQ(ret, 0);
 	self->fd = -1;
 }