selftests/mm: skip failed memfd setups in gup_longterm

selftests/mm: skip failed memfd setups in gup_longterm

Unlike the other cases gup_longterm's memfd tests previously skipped the
test when failing to set up the file descriptor to test.  Restore this
behavior to avoid hitting failures when hugetlb isn't configured.

Link: https://lkml.kernel.org/r/20250605-selftest-mm-gup-longterm-tweaks-v1-1-2fae34b05958@kernel.org
Fixes: 66bce7afbaca ("selftests/mm: fix test result reporting in gup_longterm")
Signed-off-by: Mark Brown <broonie@kernel.org>
Reported-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Closes: https://lkml.kernel.org/r/a76fc252-0fe3-4d4b-a9a1-4a2895c2680d@lucifer.local
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Tested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>