selftests/mm: soft-dirty should fail if a testcase fails

selftests/mm: soft-dirty should fail if a testcase fails

Previously soft-dirty was unconditionally exiting with success, even if
one of its testcases failed.  Let's fix that so that failure can be
reported to automated systems properly.

Link: https://lkml.kernel.org/r/20240424105301.3157695-1-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>