If HUGETLBFS is not enabled then the default_huge_page_size function will
return 0 and cause a divide by 0 error. Add a check to see if the huge page
size is 0 and skip the hugetlb tests if it is.

Link: https://lkml.kernel.org/r/20240205145055.3545806-2-terry.tritton@linaro.org
Fixes: 16a45b57 ("selftests/mm: add framework for uffd-unit-test")
Signed-off-by: Terry Tritton <terry.tritton@linaro.org>
Cc: Peter Griffin <peter.griffin@linaro.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>